Circulatory and respiratory responses to lower body negative pressure in man

Byungchul AHN, Yoshikazu SAKAKIBARA, Poul-Erik PAULEV, Atsuko MASUDA, Yoshitake NISHIBAYASHI, Wataru NAKAMURA, YOSHIYUKI HONDA
1989 The Japanese Journal of Physiology  
Circulatory and ventilatory responses to lower body negative pressure (LBNP) were simultaneously investigated in 8 healthy men before, during, and after the application of -20, -40, and -60 mmHg pressure. Minute ventilation (VE) decreased during LBNP due to a fall in respiratory frequency with sustained tidal volume. The cardiac output (Q) was reduced in proportion to the applied LBNP exposure, while VE decreased to almost the same level at all LBNP applications. In spite of decreased 1'E,
more » ... idal Poz and P~oz were increased and decreased, respectively, indicating a relative alveolar hyperventilation. The ventilation equivalent for 02 (VE/ Voz) increased, while the cardiac output equivalent for 02 (Q/ Voz) decreased. The relation between VE/ Voz and Q/ Voz showed a significant negative correlation (r = -0.93, p <0.01). The veno-arterial CO2 concentration difference (Cv~oz -Ca~oz) increased with LBNP, due to a fall in Ca~oz with constant Cv~oz. The constant CV~oz indicated a constant tissue acid-base balance. These observations suggest the existence of a ventilatory mechanism improving the efficiency of respiration in order to compensate for the sustained LBNP depression of Q at a given gas exchange.
doi:10.2170/jjphysiol.39.919 fatcat:lksu66ecpbhidpubpwgzxgizgy