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Biomedical subjects

J Pawelczyk

Publications and source records attributed to J Pawelczyk.

7 recordsLinked to original sources
PubMed1993

Effect of serotonin receptor blockade on endocrine and cardiovascular responses to head-up tilt in humans.

Effects of blockade of serotonin (5-HT) receptors on the integrated cardiovascular and endocrine adaptations during head-up tilt were investigated in normal men. In control experiments 50 degrees head-up tilt increased heart rate (HR), total peripheral resistance (TPR), plasma renin activity (PRA) and sympathetic activity (plasma noradrenaline; NA). A moderate increase in pituitary-adrenal hormones (plasma ACTH, beta-END and cortisol) was observed. After a mean tilt time of 30 +/- 5 min (n = 20) presyncopal symptoms associated with decreases in HR, TPR and arterial pressure occurred. At this time pituitary hormones, cortisol, adrenomedullary (plasma adrenaline; A) as well as vagal activity (plasma pancreatic polypeptide) were markedly increased, whereas sympathetic activity (plasma NA) decreased. The 5-HT1+2 receptor antagonist methysergide did not significantly interfere with cardiovascular variables but attenuated the response of NA, prolactin (PRL), beta-endorphin (beta-END) and PRA (P < 0.02). The 5-HT2-receptor antagonist ketanserin reduced the tolerated tilt time (10 +/- 4 vs. 32 +/- 2 min; P < 0.0003, n = 7) but had no significant effects on hormonal variables. The 5-HT3-receptor antagonist ondansetron abolished the adrenomedullary response to hypotension without affecting cardiovascular tolerance or the activity of the pituitary-adrenal axis. The results suggest that serotonergic mechanisms may be involved in the integrated cardiovascular and endocrine responses to central blood volume depletion in humans.

Adrenocorticotropic Hormone↗
PubMed1991

Oxygen consumption during fire suppression: error of heart rate estimation.

Ten male firefighters were tested on a treadmill to determine their heart rate (HR) x oxygen consumption (VO2) relationship. These men then performed a simulated fire suppression protocol during which HR and VO2 were measured simultaneously by a portable physiological monitoring system. Average VO2 in the simulated setting was 31.0 +/- 7.0 ml.kg-1.min-1 at a HR of 176 +/- 9 bpm. This VO2 was significantly (p less than or equal to 0.05) less than the VO2 that would have been predicted by treadmill testing (38.9 +/- 5.0 ml.kg-1.min-1) at a corresponding HR. Fifty-nine per cent of this variability could be accounted for by regression analysis. Firefighters worked on average at 73 +/- 10% VO2 max with a range of 54% to 88%. There was a significant (-0.82; p less than or equal to 0.05) inverse relationship between performance time of the fire suppression protocol and the relative intensity of VO2 max at which the firefighters worked. These findings indicate that the prediction of energy expenditure from HR is not straightforward in fire suppression settings. Furthermore, the relative intensity of work firefighters self-select is variable and should be considered as an additional physiological determinant of work behaviour.

Adult↗
PubMed1989

Physical performance during combinations of hypercapnic, resistive, and hot air breathing.

Performance time for a 3.2-km (2-mi) run at maximal voluntary speed was determined for 12 subjects under seven experimental conditions: resistance breathing (R), hypercapnia (C), hot air breathing (H), and combinations R + C, R + H, H + C, and R + H + C. The tests were performed on a treadmill at 5% grade. Performance time was increased significantly when the subjects were exposed to resistance breathing alone (9%) or to any combination condition containing resistance (16%-31%). The effect of breathing resistance was not specific to the presence or absence of C, H, or their combination. Nevertheless, the physiological effects were not additive and could not be predicted by knowing the effects of the individual stresses. Performance time also was increased in Condition H + C (9%). Pulmonary ventilation was the most affected physiological variable, significantly reduced in Conditions R, H, C + R, H + R, and H + C + R. In conclusion, a multistress approach should be used when determining physiological responses or performance limitations brought about by real or simulated industrial respirator-wear conditions.

Adult↗