Dwinell M R, Janssen P L, Pizarro J, Bisgard G E
Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison 53706, USA.
J Appl Physiol (1985). 1997 Jan;82(1):118-24. doi: 10.1152/jappl.1997.82.1.118.
Hypoxic ventilatory sensitivity is increased during ventilatory acclimatization to hypoxia (VAH) in awake goats, resulting in a time-dependent increase in expired ventilation (VE). The objectives of this study were to determine whether the increased carotid body (CB) hypoxic sensitivity is dependent on the level of CB CO2 and whether the CB CO2 gain is changed during VAH. Studies were carried out in adult goats with CB blood gases controlled by an extracorporeal circuit while systemic (central nervous system) blood gases were regulated independently by the level of inhaled gases. Acute VE responses to CB hypoxia (CB PO2 40 Torr) and CB hypercapnia (CB PCO2 50 and 60 Torr) were measured while systemic normoxia and isocapnia were maintained. CB PO2 was then lowered to 40 Torr for 4 h while the systemic blood gases were kept normoxic and normocapnic. During the 4-h CB hypoxia, VE increased in a time-dependent manner. Thirty minutes after return to normoxia, the ventilatory response to CB hypoxia was significantly increased compared with the initial response. The slope of the CB CO2 response was also elevated after VAH. An additional group of goats (n = 7) was studied with a similar protocol, except that CB PCO2 was lowered throughout the 4-h CB hypoxic exposure to prevent reflex hyperventilation. CB PCO2 was progressively lowered throughout the 4-h CB hypoxic period to maintain VE at the control level. After the 4-h CB hypoxic exposure, the ventilatory response to hypoxia was also significantly elevated. However, the slope of the CB CO2 response was not elevated after the 4-h hypoxic exposure. These results suggest that CB sensitivity to both O2 and CO2 is increased after 4 h of CB hypoxia with systemic isocapnia. The increase in CB hypoxic sensitivity is not dependent on the level of CB CO2 maintained during the 4-h hypoxic period.
在清醒山羊对低氧的通气适应（VAH）过程中，低氧通气敏感性增加，导致呼出通气量（VE）随时间增加。本研究的目的是确定颈动脉体（CB）低氧敏感性的增加是否依赖于CB的二氧化碳水平，以及在VAH期间CB的二氧化碳增益是否发生变化。研究在成年山羊中进行，通过体外循环控制CB的血气，而全身（中枢神经系统）的血气则通过吸入气体水平独立调节。在维持全身常氧和等碳酸血症的同时，测量对CB低氧（CB PO2 40 Torr）和CB高碳酸血症（CB PCO2 50和60 Torr）的急性VE反应。然后将CB PO2降至40 Torr持续4小时，同时将全身血气维持在常氧和常碳酸水平。在4小时的CB低氧期间，VE呈时间依赖性增加。恢复常氧30分钟后，与初始反应相比，对CB低氧的通气反应显著增加。VAH后CB二氧化碳反应的斜率也升高。另一组山羊（n = 7）采用类似方案进行研究，不同之处在于在整个4小时的CB低氧暴露期间降低CB PCO2以防止反射性过度通气。在整个4小时的CB低氧期，CB PCO2逐渐降低以将VE维持在对照水平。在4小时的CB低氧暴露后，对低氧的通气反应也显著升高。然而，4小时低氧暴露后CB二氧化碳反应斜率未升高。这些结果表明，在全身等碳酸血症的情况下，CB低氧4小时后对O2和CO2的敏感性均增加。CB低氧敏感性的增加不依赖于4小时低氧期维持的CB CO2水平。
