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Baroreflex gain and time of pressure decay at different body temperatures in the tegu lizard, Salvator merianae

  • Renato Filogonio ,

    Roles Conceptualization, Formal analysis, Investigation, Methodology, Project administration, Supervision, Validation, Writing – original draft, Writing – review & editing

    Affiliation Department of Physiological Sciences, Federal University of São Carlos, São Carlos, São Paulo, Brazil

  • Karina F. Orsolini,

    Roles Conceptualization, Formal analysis, Investigation, Methodology, Visualization, Writing – review & editing

    Affiliation Department of Physiological Sciences, Federal University of São Carlos, São Carlos, São Paulo, Brazil

  • Gustavo M. Oda,

    Roles Data curation, Investigation, Methodology, Writing – review & editing

    Affiliation Department of Physiological Sciences, Federal University of São Carlos, São Carlos, São Paulo, Brazil

  • Hans Malte,

    Roles Formal analysis, Methodology, Validation, Writing – review & editing

    Affiliation Section for Zoophysiology, Department of Bioscience, Aarhus University, Aarhus C, Denmark

  • Cléo A. C. Leite

    Roles Conceptualization, Data curation, Funding acquisition, Methodology, Project administration, Resources, Supervision, Visualization, Writing – original draft, Writing – review & editing

    Affiliation Department of Physiological Sciences, Federal University of São Carlos, São Carlos, São Paulo, Brazil

Baroreflex gain and time of pressure decay at different body temperatures in the tegu lizard, Salvator merianae

  • Renato Filogonio, 
  • Karina F. Orsolini, 
  • Gustavo M. Oda, 
  • Hans Malte, 
  • Cléo A. C. Leite


Ectotherms may experience large body temperature (Tb) variations. Higher Tb have been reported to increase baroreflex sensitivity in ectotherm tetrapods. At lower Tb, pulse interval (PI) increases and diastolic pressure decays for longer, possibly resulting in lower end-diastolic pressures and mean arterial pressures (Pm). Additionally, compensatory baroreflex-related heart rate modulation (i.e. the cardiac branch of the baroreflex response) is delayed due to increased PI. Thus, low Tb is potentially detrimental, leading to cardiovascular malfunctioning. This raises the question on how Pm is regulated in such an adverse condition. We investigated the baroreflex compensations that enables tegu lizards, Salvator merianae, to maintain blood pressure homeostasis in a wide Tb range. Lizards had their femoral artery cannulated and pressure signals recorded at 15°C, 25°C and 35°C. We used the sequence method to analyse the heart rate baroreflex-related corrections to spontaneous pressure fluctuations at each temperature. Vascular adjustments (i.e. the peripheral branch) were assessed by calculating the time constant for arterial pressure decay (τ)—resultant from the action of both vascular resistance and compliance—by fitting the diastolic pressure descent to the two-element Windkessel equation. We observed that at lower Tb, lizards increased baroreflex gain at the operating point (Gop) and τ, indicating that the diastolic pressure decays at a slower rate. Gop normalized to Pm and PI, as well as the ratio τ/PI, did not change, indicating that both baroreflex gain and rate of pressure decay are adjusted according to PI lengthening. Consequently, pressure parameters and the oscillatory power fraction (an index of wasted cardiac energy) were unaltered by Tb, indicating that both Gop and τ modulation are crucial for cardiovascular homeostasis.


Temperature is possibly the most important abiotic factor affecting the physiology of ectotherms [1]. Increased body temperature (Tb) is associated with higher heart rate (fH) and cardiac output [27], although mean arterial pressures (Pm) are less affected [4,79]. In vertebrates, acute changes in arterial blood pressure are regulated by the baroreflex mechanism [10]. The cardiac branch of the baroreflex response is expressed as baroreflex gain (i.e. the heart rate variation per unit of pressure change [11]). The maximum baroreflex gain (G50) is temperature-sensitive in amphibians [7] and reptiles [12], and exhibits higher values at elevated Tb.

At lower Tb, the increased pulse interval (PI) resultant from lower fH necessarily imply delayed and slower baroreflex-related fH modulations to rapid arterial pressure variations. Additionally, the extended interval between heartbeats allows for elongated periods of diastolic pressure decay, potentiating the likelihood for hypotension. Under these circumstances, an inefficient response of the cardiac branch of the baroreflex mechanism could result in a hindered tissue perfusion. Notwithstanding, free-ranging amphibians and reptiles experience a broad range of Tb [1,1322] without any apparent cardiovascular malfunction or homeostasis impairment. Therefore, other mechanisms must compensate for the loss of efficiency of the cardiac branch of the baroreflex at low Tb.

We speculated that the vascular branch of the baroreflex could assist the cardiac branch in sustaining the cardiovascular homeostasis when Tb reduces. One way of assessing vascular regulation is by analyzing the rate of diastolic pressure decay (i.e. the time constant for arterial pressure decay during diastole: τ; Fig 1A), which is the result of the action of both vascular resistance and compliance when aortic valves close [23]. We expected that, since vascular resistance increases at colder Tb [4,8], diastolic pressure (Pd) should exhibit a slower decline, thus avoiding hypotension. In addition, a slower pressure decay could minimize pressure oscillations around Pm at lower Tb, thus reducing the relative “wasted” cardiac energy (i.e. the oscillatory power fraction–OPF [24]). Therefore, we postulated that the control of the vascular system by the peripheral branch of the baroreflex would compensate the loss of efficiency of the cardiac branch in maintaining pressure homeostasis by regulating τ according to PI lengthening. This could prevent both hypotension and larger oscillations of blood pressure when Tb decreases.

Fig 1. Representative original pressure traces recorded from tegu lizards, Salvator merianae.

A) Pressure (in kPa) of a S. merianae recorded at 15°C (n = 1). The scheme indicates the peak systolic pressure (Ps), end-diastolic pressure (Pd), pulse pressure (Pp), mean arterial pressure (Pm; closed circle), diastolic pressure decay (red broken line), and pulse interval. B) Pressure (in kPa) recorded at 15°C (grey line), 25°C (blue line) and 35°C (red line) (n = 1). C) Example of estimated pressure decay using the Windkessel equation (black lines), based at the diastolic pressure recorded at 15°C (grey line), 25°C (blue line) and 35°C (red line) (n = 3).

The present study was designed to investigate putative functional adjustments of both cardiac and peripheral branches of the baroreflex that allow effective pressure regulation in a range of Tb experienced by the tegu lizard, Salvator merianae. The study was conducted during the non-reproductive period of the species, when facultative endothermy is not manifested and Tb varies as a typical ectotherm lizard [25]. We used the sequence method to assess baroreflex gain at the operating point (Gop; i.e. gain at the point of the baroreflex sigmoidal curve correspondent to the Pm operating point [26]) and baroreflex effectiveness index (BEI; i.e. the capacity of the baroreflex to overcome concomitant stimuli modulating fH [27,28]) to investigate the responses of the cardiac branch. Since longer PI at lower Tb enables pressure to decay for longer times, it is possible that Gop is adjusted to protect against hypotensive episodes. We also investigated τ and the ratio τ/PI as an estimate of vascular regulation at different Tb. We predicted that in order to preserve systemic functionality, τ and PI should variate accordingly as to maintain τ/PI and OPF relatively constant. Hence, baroreflex should trigger compensatory adjustments that involve both cardiac and vascular responses to Tb changes in S. merianae.

Material and methods

Animal acquisition and maintenance

Eleven juvenile tegu lizards (Salvator merianae, mean mass ± standard deviation: 622.7 ± 90.6 g) were donated by the Jacarezário (UNESP–Rio Claro, Brazil), and maintained at the facilities of the Laboratory of Experimental Biology (UFSCar–São Carlos, Brazil). Animals were kept in groups of four to five individuals at 1.2 × 0.8 × 0.8 m tanks with access to heating lamps, under a natural light regime ~12:12 h. Tegu lizards were fed on eggs and chicken liver and had access to ad libitum water supply. Feeding was interrupted for five days (equivalent to the postprandial duration after 10% of body mass ingestion in S. merianae maintained at 30°C [29]) prior to experimental procedures to avoid SDA effect on the cardiovascular parameters.


Before surgical procedures, lizards were sedated with elevated levels of CO2 until complete loss of righting reflexes [28,3033]. Individuals underwent tracheal intubation and were mechanically ventilated with isoflurane (2–5%; 5 breaths × min-1; tidal volume of 30 ml × kg-1; SAR-830/P Ventilator) throughout the entire surgical procedure. A heating cushion set to 30°C was used to maintain a stable body temperature. Local anaesthetic (Lidocaine 2%, Pearson; 10 mg × kg-1) was injected in the left thigh before a 3 cm longitudinal incision was made. The femoral artery was occlusively cannulated with a P50 catheter filled with heparinized saline (50 IU × ml-1). Lizards were injected with antibiotic (Chemitril, 11mg × kg-1) and anti-inflammatory/analgesic (Flunixin 1.1mg × kg-1) just after the surgical procedure, and after every 48 hours for four days. All procedures were performed under sterile conditions. Animals were allowed to recover in a temperature-controlled chamber set to 35°C (which is within the species’ preferred body temperature range [25,34]) in a maintenance container (25 × 35 × 10 cm). Experimental protocols started five days after the instrumentation surgery, which corresponds to the recovery time of the resting pattern of autonomic modulation after instrumentation in S. merianae [30].

Before measurements, the catheter was connected to a Baxter Edward (model PX600, Irvine, CA, USA) disposable pressure transducer and signals were amplified with a single-channel preamplifier (Bridge Amp, ADInstruments) before being connected to a Power Lab® data acquisition system (ADInstruments). Pressure transducers were daily calibrated against a static water column before measurements using LabChart® software (LabChart v.7.0, ADInstruments).

Throughout the recovery period, the catheter was washed with sterile heparinised saline and signal quality was evaluated in order to check for any signal loss. During the protocol, lizards were exposed to one of the three experimental temperatures (35, 25 or 15°C) each day, in a decreasing order. Lizards were given 24 h to allow Tb stabilization at each set temperature before pressure recording. Tattersall et al. [25] reports that adult tegu lizards (~ 2000 g) require less than 10 h to cool down approximately 14°C inside their burrows. Therefore, the 24 h interval between measurements in the present study was sufficient for lizards to stabilize their Tb with the set environmental temperature. Accordingly, blood pressure traces were recorded for 2–3 h from autonomic recovered resting lizards at different Tb encompassing the temperature range most commonly experienced by S. merianae [25].

By the end of the protocol, lizards were anaesthetized and euthanized by injection of thiopenthal (Thiopentax, Cristália; 50 mg × kg-1), followed by an i.v. injection of a saturated K+ solution until the heart stopped beating. All procedures were performed in accordance with guidelines from the Brazilian National Council for the Control of Animal Experimentation (CONCEA), and approved by the Ethics Committee on Animal Use of the Federal University of São Carlos (CEUA/UFSCar n° 4663270916).

Data analysis

Before analysis, pressure signals were filtered using a low pass (20Hz) digital filter. For each temperature tested, peak systolic and end-diastolic arterial pressures (Ps and Pd, respectively), heart rate (fH) and pulse interval (PI) were obtained using the distance between consecutive diastolic pressures (Fig 1A). Mean arterial pressure (Pm) was calculated as Pd + (PsPd) / 3, whereas pulse pressure (Pp) was the difference between Ps and Pd (Fig 1A) [35].

We utilized the sequence method to assesses the baroreflex at the operating point (Gop) based on the average of the slopes from spontaneous baroreflex sequences (i.e. minimum of three cardiac cycles displaying sequential increases or decreases in Ps followed by concomitant modulation of PI [27,28,36]). Baroreflex gain obtained was then normalized for Pm and PI to allow for meaningful comparisons between temperatures [37,38]: (1)

Baroreflex effectiveness index (BEI) was calculated as a ratio between the number of baroreflex sequences and the total number of ramps, which comprise both baroreflex and non-baroreflex sequences [27,28]: (2)

These calculations were performed with CardioSeries software (v2.4, utilizing a minimum of 300 cardiac cycles and delay 1 [28].

To assess the putative regulation of the vascular system to different Tb, we calculated the time constant of arterial pressure decay during diastole (τ; Fig 1A). We fitted a representative portion of the second half of the diastolic pressure curve to a modified two-element Windkessel equation based on Westerhof et al. [23]: (3) Where P(t) is diastolic pressure at time t, P0 is end-systolic pressure, and A is the asymptote [23,39,40]. Values were fitted using GraphPad Prism v.7.00.

We calculated oscillatory power fraction (OPF) as determined by Saouti et al. [24]: (4)

Data were analysed using one-way ANOVA for repeated measures using temperature as factor followed by Tukey post hoc test using SigmaPlot (v. 11). Normality was assessed with a Kolmogorov-Smirnov test. Statistical significance was assigned as P < 0.05. Data are presented as mean ± standard deviation.

Results and discussion

Acknowledging that adult S. merianae produce internal heat during the reproductive season [25], we studied juveniles during the non-reproductive period to avoid this confounding factor. Nonetheless, it is worth noting that the preferred Tb of S. merianae does not depend on size or reproductive condition [34]. Heart rate exhibited the typical increase with Tb as observed in other reptiles [3,8,41,42], with the concomitant decrease in PI (Table 1; Fig 1B). In a recent investigation, O2 consumption of tegu lizards increased about 4-fold between 17°C and 37°C [43], and fH followed a similar pattern in the present study. This indicates that cardiac output regulation supporting metabolic alteration triggered by temperature change is mainly governed by fH modulation. The close relationship between fH and metabolic rate has been experimentally evidenced for S. merianae [43]. Despite the magnitude of those alterations, none of the pressure parameters changed with Tb (Table 1). This agrees with results reported for the freshwater turtle Trachemys scripta, where Pm remains unchanged upon Tb variation [4].

Table 1. Temperature effects on the hemodynamic variables.

Gop was the lowest when measured at 35°C (Table 1). This result is in stark contrast with those from other ectotherms, where baroreflex sensitivity was shown to increase with temperature [7,12]. This may be due to differences between the sequence method and the pharmacological method (i.e. the Oxford method) regarding the calculation of baroreflex gain. The sequence method used in the present study estimates baroreflex gain close to the Pm at the operating point, whereas the pharmacological method used in previous studies [7,12,38,44,45] calculates maximum gain [26]. The Pm at the operating point for S. merianae was estimated to be higher than Pm at the midpoint of the fH baroreflex response range [44], which is used to calculate G50 [46]. Therefore, the two methods estimate gain at different regions of the baroreflex response curve (Fig 2). A steeper slope at the midpoint of the fH baroreflex response range increases G50. We speculate that, when Tb increases, the slope of the baroreflex sigmoidal curve at the operating point decreases, whereas the slope at the midpoint of the fH baroreflex response range increases at the same conditions (Fig 2). In this way, it is possible that increased Tb could induce reductions in Gop at the same time G50 increases.

Fig 2. Schematic figure comparing baroreflex sensitivity assessed by two different methods.

The sigmoidal baroreflex curves represent a theoretical response to body temperature (Tb) changes. The sequence method estimates gain at the operating point (Gop; red circle), whereas the pharmacological method estimates maximum gain (G50; blue circle). The slope at the specific point of the curves are in red for Gop, and blue for G50. Note that, while the slope at Gop is less inclined at higher Tb, slope at G50 is steeper.

Nonetheless, the higher Gop at 15°C and 25°C indicates the sensitivity for correction of arterial pressure perturbations are enhanced. Since longer PI leaves more time for pressure to decay, it is possible that this increased Gop helps S. merianae to better protect against hypotension. The unaltered normalized gain values (Gnorm; Table 1) indicate that the baroreflex sensitivity in the tegu lizard is actively optimized to work at the different fH and blood pressure conditions imposed by different Tb. This is further substantiated by the unaltered BEI over temperature changes (Table 1).

The two-element Windkessel model (Eq 3) fitted well to our dataset (R2 > 0.999; Fig 1C). Increased temperatures led to decreased τ (Table 1), probably as a result of reduced arterial resistance [4,8,47], indicating pressure during diastole falls faster at 25°C and 35°C. However, the ratio τ/PI was similar at all temperatures tested (Table 1), meaning that the time for pressure decay was proportional to pulse interval. A constant relationship between τ and PI was also observed for mammals where fH decreases as an effect of scaling with body size, and was argued as the reason why Pp and Pd were unaltered [48]. Likewise, the constant Pp and Pd exhibited by S. merianae in the present study are probably the result of the proportional changes of τ related to PI. This conclusion was supported by the unvarying OPF at all temperatures (Table 1), indicating that the relative energy expended by the heart at each cardiac cycle remains constant (~18–20% energetic waste) throughout the temperature gradient experienced by resting S. merianae in our experiments.

The present study was the first to evaluate the efficiency of the orchestrated baroreflex response from both heart rate and vascular regulation to temperature variations in an ectotherm vertebrate. Here, we demonstrated that both responses are adjusted in concert to regulate the arterial blood pressure at different Tb. For example, Gop was exacerbated when Tb dropped from 35°C to 25°C, possibly as a stronger response to hypotension since pressure decayed for longer and τ was similar between these two Tb. On the other hand, τ increased when Tb reduced from 25°C to 15°C, while Gop remained unchanged. Those adjustments ensured similar Pm at all Tb tested, and prevented the amplification of pressure oscillations when PI increased, thus minimizing the cyclic waste of cardiac energy. Therefore, the present data underlines the fundamental role of the vascular regulation, in addition to the baroreflex-related heart rate response, in sustaining blood pressure homeostasis and cardiac efficiency of S. merianae at different Tb.


Augusto S. Abe from the Jacarezário (UNESP-Rio Claro) gently donated the animals for this study. We are also thankful to Samanta A. Castro and Driele Tavares for assistance during surgical procedures. Lucas A. Zena and Ana L. Kalinin kindly commented on an early draft of the manuscript.


  1. 1. Seebacher F. A review of thermoregulation and physiological performance in reptiles: what is the role of phenotypic flexibility? J Comp Physiol B. 2005;175: 453–461. pmid:16034580
  2. 2. Filogonio R, Taylor EW, Carreira LBT, Leite GSPC, Abe AS, Leite CAC. Systemic blood flow relations in conscious South American rattlesnakes. South Am J Herpetol. 2014;9: 171–176.
  3. 3. Filogonio R, Wang T, Taylor EW, Abe AS, Leite CAC. Vagal tone regulates cardiac shunts during activity and at low temperatures in the South American rattlesnake, Crotalus durissus. J Comp Physiol B. 2016;186: 1059–1066. pmid:27294346
  4. 4. Galli G, Taylor E, Wang T. The cardiovascular responses of the freshwater turtle Trachemys scripta to warming and cooling. J Exp Biol. 2004;207: 1471–1478. pmid:15037641
  5. 5. Hedrick MS, Palioca WB, Hillman SS. Effects of temperature and physical activity on blood flow shunts and intracardiac mixing in the toad Bufo marinus. Physiol Biochem Zool. 1999;72: 509–519. pmid:10521319
  6. 6. Kalinin AL, Costa MJ, Rantin FT, Glass ML. Effects of temperature on cardiac function in teleost fish. In: Glass ML, Wood SC, editors. Cardio-Respiratory Control in Vertebrates. Berlin, Heidelberg: Springer Berlin Heidelberg; 2009. pp. 121–160.
  7. 7. Zena LA, Gargaglioni LH, Bícego KC. Temperature effects on baroreflex control of heart rate in the toad, Rhinella schneideri. Comp Biochem Physiol A Mol Integr Physiol. 2015;179: 81–88. pmid:25263128
  8. 8. Stinner JN. Cardiovascular and metabolic responses to temperature in Coluber constrictor. Am J Physiol-Regul Integr Comp Physiol. 1987;253: R222–R227. pmid:3618822
  9. 9. Lillywhite HB, Seymour RS. Regulation of arterial blood pressure in Australian tiger snakes. J Exp Biol. 1978;75: 65–79. pmid:702045
  10. 10. Bagshaw RJ. Evolution of cardiovascular baroreceptor control. Biol Rev. 1985;60: 121–162. pmid:3890977
  11. 11. Swenne CA. Baroreflex sensitivity: mechanisms and measurement. Neth Heart J. 2013;21: 58–60. pmid:23179611
  12. 12. Hagensen MK, Abe AS, Wang T. Baroreflex control of heart rate in the broad-nosed caiman Caiman latirostris is temperature dependent. Comp Biochem Physiol A Mol Integr Physiol. 2010;156: 458–462. pmid:20363351
  13. 13. Cowles RB, Bogert CM. A preliminary study of the thermal requirements of desert reptiles. Bull Am Mus Nat Hist. 1944;83: 261–296.
  14. 14. Filogonio R, Coutinho ME, Abe AS. Thermoregulation of captive Caiman latirostris (Alligatoridae). Herpetol Notes. 2014;7: 619–622.
  15. 15. Huey RB. Temperature, Physiology, and the Ecology of Reptiles. Biology of the Reptilia, Vol 12, Physiology (C). 1982. pp. 25–91.
  16. 16. Filogonio R, Wang T, Abe AS, Leite CAC. Cooling and warming rates are unaffected by autonomic vascular control in the south American rattlesnake (Crotalus durissus). South Am J Herpetol. 2019;14: 242.
  17. 17. Rocha CFD. Introdução à ecologia de lagartos brasileiros. 1st ed. Herpetologia no Brasil 1. 1st ed. Minas Gerais: Fundação Biodiversitas / PUC-MG / Fundação Ezequiel Dias / FAPEMIG; 1994. pp. 39–57.
  18. 18. Tozetti AM, Martins M. Habitat use by the South‐American rattlesnake (Crotalus durissus) in south‐eastern Brazil. J Nat Hist. 2008;42: 1435–1444.
  19. 19. Carey C. Factors affecting body temperature in toads. Oecologia. 1978;35: 197–219. pmid:28309733
  20. 20. Navas CA, Antoniazzi MM, Jared C. A preliminary assessment of anuran physiological and morphological adaptation to the Caatinga, a Brazilian semi-arid environment. Int Congr Ser. 2004;1275: 298–305.
  21. 21. Warburg MR. Ecophysiology of amphibians inhabiting xeric environments. Berlin, Germany: Springer-Verlag; 1997.
  22. 22. Burrowes PA, Navas CA, Jiménez-Robles O, Delgado P, De la Riva I. Climatic heterogeneity in the Bolivian Andes: are frogs trapped? South Am J Herpetol. 2020;18: 1.
  23. 23. Westerhof N, Lankhaar J-W, Westerhof BE. The arterial Windkessel. Med Biol Eng Comput. 2009;47: 131–141. pmid:18543011
  24. 24. Saouti N, Westerhof N, Helderman F, Marcus JT, Boonstra A, Postmus PE, et al. Right ventricular oscillatory power is a constant fraction of total power irrespective of pulmonary artery pressure. Am J Respir Crit Care Med. 2010;182: 1315–1320. pmid:20622041
  25. 25. Tattersall GJ, Leite CAC, Sanders CE, Cadena V, Andrade DV, Abe AS, et al. Seasonal reproductive endothermy in tegu lizards. Sci Adv. 2016;2: e1500951. pmid:26844295
  26. 26. Raven PB, Fadel PJ, Ogoh S. Arterial baroreflex resetting during exercise: a current perspective. Exp Physiol. 2006;91: 37–49. pmid:16210446
  27. 27. Di Rienzo M, Parati G, Castiglioni P, Tordi R, Mancia G, Pedotti A. Baroreflex effectiveness index: an additional measure of baroreflex control of heart rate in daily life. Am J Physiol-Regul Integr Comp Physiol. 2001;280: R744–R751. pmid:11171653
  28. 28. Filogonio R, Orsolini KF, Castro SA, Oda GM, Rocha GC, Tavares D, et al. Evaluation of the sequence method as a tool to assess spontaneous baroreflex in reptiles. J Exp Zool Part Ecol Integr Physiol. 2019;331: 374–381. pmid:31180622
  29. 29. Gavira RSB, Sartori MR, Gontero-Fourcade MN, Gomes BF, Abe AS, Andrade DV. The consequences of seasonal fasting during the dormancy of tegu lizards (Salvator merianae) on their postprandial metabolic response. J Exp Biol. 2018;221: jeb176156. pmid:29530973
  30. 30. Duran LM, Taylor E, Sanches PVW, Cruz AL, Tavares D, Sartori MR, et al. Heart rate variability in the tegu lizard, Salvator merianae, its neuroanatomical basis and role in the assessment of recovery from experimental manipulation. Comp Biochem Physiol A Mol Integr Physiol. 2020;240: 110607. pmid:31707060
  31. 31. Leite CAC, Taylor EW, Wang T, Abe AS, de Andrade DOV. Ablation of the ability to control the right-to-left cardiac shunt does not affect oxygen uptake, specific dynamic action or growth in the rattlesnake Crotalus durissus. J Exp Biol. 2013;216: 1881–1889. pmid:23393283
  32. 32. Leite CAC, Wang T, Taylor EW, Abe AS, Leite GSPC, de Andrade DOV. Loss of the ability to control right-to-left shunt does not influence the metabolic responses to temperature change or long-term fasting in the South American rattlesnake Crotalus durissus. Physiol Biochem Zool. 2014;87: 568–575. pmid:24940921
  33. 33. Wang T, Fernandes W, Abe AS. Blood pH and O2 homeostasis upon CO2 anesthesia in the rattlesnake (Crotalus durissus). The Snake. 1993;25: 21–26.
  34. 34. Cecchetto NR, Naretto S. Do sex, body size and reproductive condition influence the thermal preferences of a large lizard? A study in Tupinambis merianae. J Therm Biol. 2015;53: 198–204. pmid:26590472
  35. 35. Klabunde RE. Cardiovascular physiology concepts. 2nd ed. Lippincot Williams & Wilkins; 2005.
  36. 36. Bertinieri G, Di Rienzo M, Cavalazzi A, Ferrari AU, Pedotti A, Mancia G. Evaluation of baroreceptor reflex by blood pressure monitoring in unanesthetized cats. Am J Physiol-Heart Circ Physiol. 1988;23: H377–H383. pmid:3344828
  37. 37. Berger PJ, Evans BK, Smith DG. Localization of baroreceptors and gain of the baroreceptor-heart rate reflex in the lizard Trachydosaurus rugosus. J Exp Biol. 1980;89: 197–209.
  38. 38. Crossley DA, Hicks JW, Altimiras J. Ontogeny of baroreflex control in the American alligator Alligator mississippiensis. J Exp Biol. 2003;206: 2895–2902. pmid:12847132
  39. 39. Reuben SR. Compliance of the human pulmonary arterial system in disease. Circ Res. 1971;29: 40–50. pmid:5561407
  40. 40. Chemla D, Lau EMT, Hervé P, Millasseau S, Brahimi M, Zhu K, et al. Influence of critical closing pressure on systemic vascular resistance and total arterial compliance: a clinical invasive study. Arch Cardiovasc Dis. 2017;110: 659–666. pmid:28958408
  41. 41. Clark TD, Wang T, Butler PJ, Frappell PB. Factorial scopes of cardio-metabolic variables remain constant with changes in body temperature in the varanid lizard, Varanus rosenbergi. Am J Physiol-Regul Integr Comp Physiol. 2005;288: R992–R997. pmid:15576663
  42. 42. Tucker VA. Oxygen transport by the circulatory system of the green iguana (Iguana iguana) at different body temperatures. J Exp Biol. 1966;44: 77–92. pmid:5922740
  43. 43. Piercy J, Rogers K, Reichert M, Andrade DV, Abe AS, Tattersall GJ, et al. The relationship between body temperature, heart rate, breathing rate, and rate of oxygen consumption, in the tegu lizard (Tupinambis merianae) at various levels of activity. J Comp Physiol B. 2015;185: 891–903. pmid:26285591
  44. 44. Zena LA, Dantonio V, Gargaglioni LH, Andrade DV, Abe AS, Bícego KC. Winter metabolic depression does not change arterial baroreflex control of heart rate in the tegu lizard Salvator merianae. J Exp Biol. 2016;219: 725–733. pmid:26747909
  45. 45. Altimiras J, Franklin CE, Axelsson M. Relationships between blood pressure and heart rate in the saltwater crocodile Crocodylus porosus. J Exp Biol. 1998;201: 2235–2242. pmid:9662494
  46. 46. Wong J, Chou L, Reid IA. Role of AT1 receptors in the resetting of the baroreflex control of heart rate by angiotensin 11 in the rabbit. J Clin Invest. 1993;91: 1516–1520. pmid:8473497
  47. 47. Stecyk JAW, Overgaard J, Farrell AP, Wang T. α-Adrenergic regulation of systemic peripheral resistance and blood flow distribution in the turtle Trachemys scripta during anoxic submergence at 5°C and 21°C. J Exp Biol. 2004;207: 269–283.
  48. 48. Westerhof N, Elzinga G. Normalized input impedance and arterial decay time over heart period are independent of animal size. Am J Physiol-Regul Integr Comp Physiol. 1991;261: R126–R133. pmid:1858938