Physiologische Veränderungen der peripheren arteriellen Tonometrie (PAT-Signal) unter Hypoxie- und Hyperkapniebedingungen

This study examined the influence of a long term (20 minutes) isocapnic hypoxia (O2 saturation = 80 %) and hyperoxic hypercapnia (Read-test) on peripheral vascular tone, which is recorded plethysmographically by means of peripheral arterial tonometry (PAT). The PAT signal represents sympathetic tone. Moreover the relation between PAT-amplitude and blood pressure will be examined. Twenty-three awake and healthy volunteers (mean age 23. 8 ± 2.1 years, BMI 22.63 ± 2.58 kg/m2) were investigated using a special closed loop breathing analysis machine developed in Marburg. During the transitional phase between room air breathing and hypoxia a significant decrease of the PAT amplitude from 0.568 ± 0.570 mV to 0.494 ± 0.501 mV was found. Related to the preceding room air breathing phase, the PAT amplitude was reduced by 12.98 % (p=0.0082). During this phase likewise a significant enhancement of inspiratory respiratory volume (p<0.0001), diastolic blood pressure (p=0.0385), systolic blood pressure (p=0.0171), and heart rate (p<0.0001) was found. On Average the PAT amplitude remained diminished during the entire hypoxia phase. But during the hypoxia phase PAT amplitude almost returned to base line level. A significant reduction compared to room air was detected only during the first 5 minutes (0.494 ± 0.495 mV, p= 0.0249). Compared to isocapnic hypoxia, the hyperoxic hypercapnia did produce a stronger reduction of PAT amplitude during the preceding resting phase (from 0.551 ± 0.546 mV to 0.346 ± 0.302 mV), which corresponds to a significant decrease of 22.4% (p=0.0005). Compared with base line level, inspiratory respiratory volume (p<0.0001), systolic (p<0.0001), and diastolic blood pressure (p<0.0001) were significantly elevated both during the hypoxia and during the hyperoxic hypercapnia. Both between systolic blood pressure and PAT-amplitude and diastolic blood pressure and PAT amplitude there were strong negative correlations. Based on our results it can not be concluded that a stronger correlation exists between diastolic blood pressure and PAT signal compared to systolic blood pressure and PAT signal. The peripheral arterial tonometry is well suited to detect hypoxia events. In this study, the effect of hypercapnia on the PAT signal could not be separated from the effect of the hypoxia on the PAT signal. In conclusion the PAT signal can be used for the detection of short repetitive hypoxia episodes, as they occur with sleep related breathing disorders.