Fig 1.
Schematic description of continuous real-time breath analysis.
a) Participants breathed through a sterile mouthpiece without resistance. Ex- and inhaled breath was transferred continuously into the heated transfer line (connected via t-piece) of the PTR-ToF-MS in a side-stream mode at a flow of 20 ml/min. b) Every 200 ms a TOF—mass spectrum was recorded. c) Profiles of breath VOCs could be recorded continuously and in a phase resolved way. Acetone (red curve 59.049 m/z—as endogenous, blood borne VOC) was used to track breath phases and to assign all other mass traces to alveolar (red areas) and inhalation (blue areas) phases. In this way, intensities of VOCs other than acetone, such as isoprene (pink curve, 69.070 m/z) or dimethyl sulfide (blue curve, 63.026 m/z) could be assigned to the different breath phases and quantified in alveolar and inspiratory air.
Table 1.
Anthropometric data of the study population and relevant medications in CKD patients.
Table 2.
Clinical characteristics of patients.
Data is given as median and range. Superscripts denote significant differences between identically labelled groups.
Fig 2.
Heat map (A) and PCA score (B) obtained in CKD patients (n = 56) and controls (n = 60).
A: Heat map based on normalized data of 71 mass traces (18 to 373 m/z) in breath of CKD patients (left) and healthy controls (right). Regions with elevated breath VOC levels are shown as red and yellow boxes for patients and controls, respectively. B: PCA score plot (PC-1 vs. PC-2) of healthy controls (blue squares, n = 60) and CKD patients (red dots, n = 56). Red circles represent data from patients with a functional renal transplant.
Table 3.
Exhaled alveolar concentrations of selected VOC in the study population.
Fig 3.
Exhaled alveolar concentrations of ammonia, ethanol, methylamine, isoprene, pentanal and heptanal in healthy controls (Co, n = 60) and CKD patients (n = 56).
Box plots were used to summarize data from controls, KTx patients and those with mild (CKD stage 1) and moderate (CKD stages 2–4) disease. Significant differences between groups are indicated (**, p < 0.001; *, p < 0.01; #, p<0.05).
Fig 4.
Exhaled alveolar concentrations of isoprene relative to the BMI in controls (blue circles) and patients (red circles).
Controls (n = 60): r = 0.53, p < 0.001; patients (n = 56): r = 0.47, p<0.001.
Fig 5.
Exhaled alveolar concentrations of ammonia, ethanol, methylamine, isoprene, pentanal and heptanal relative to the eGFR in CKD patients (n = 56).