Poor ventilatory response to mild hypoxia may inhibit acclimatization at moderate altitude in elderly patients after carotid surgery.

Abstract

Peripheral chemoreceptors (carotid bodies) are the main sensing organs for hypoxaemia. During carotid surgery, the carotic body in the bifurcation of the common carotid artery is often involved and damaged or destroyed. Animals lose their ability to adapt to high altitude after experimental denervation of the carotid bodies. The objective of our study was to responds to hypoxaemia and not to anaemia or reduced flow. It is, therefore, the main organ for transduction of hypoxic signals in altitude and inducing hypoxic ventilatory response. In animal experiments, after removal or denervation of both carotid bodies, acute hypoxia actually causes depression of ventilation3. Up to now, no data have been reported on the altitude adaptation of patients after carotid surgery with possible involvement and damage of the carotic body.The objective of our study was to evaluate the acute ventilatory adaptation in moderate altitude of patients after carotid surgery. Patients and methodsThis study was performed in the Austrian Alps at moderate altitude. Five patients participated after informed consent. Four male and one female patient, mean(s.d.) age 70(3.21) years at the time of operation, had elective carotid surgery because of severe symptomatic stenosis of the internal carotid. All five patients had a history of hypertension; no patient suffered from COPD or asthma; and all patients were ex-smokers for more than 2 years. No patient took part in a special training programme, all five estimated their physical fitness to be average, all were in a good state of health after the operation and able to go for walks on foot, and all were lowland dwellers. Before (interval 2 weeks -2 months) and after (interval 6 months-15 months) carotid surgery, capillary blood was obtained from the arterialized ear lobe of each patient4 at 171 m altitude. After passive transport by car to 1600 m and 45 min rest, the same procedure was repeated. Blood samples were stored in an ice water cooling box and analysed on a BGE Blood Gas Analyser (Instrumentation Laboratory, Milano, Italy) within 2 h. Samples were taken between 0900 and 1100 at similar conditions, ambient temperature was constant at 21°C at 171 m (air conditioned university clinic) and 18°C at 1600 m (mountain restaurant). Breathing frequency and blood pressure were also recorded at each sampling.

Peripheral chemoreceptors in health and disease

“…Barnard et al (4) also reported increased carotid body activity in cats exposed to hypoxia for 28 days. Furthermore, human subjects who have undergone carotid surgery adapt rather poorly to high altitude (72), further supporting the idea that chemoreflexes are necessary for altitude acclimatization. Tatsumi et al (84) reported decreased responsiveness of the carotid bodies and hypoxic ventilatory response in cats after 3-4 wk of exposure to 5,500-m altitude, suggesting that prolonged altitude exposure leads to diminished ventilatory hypoxic sensitivity, which is in part due to "desensitization" of the carotid body O 2 -sensing mechanisms (92).…”

Adaptive and Maladaptive Cardiorespiratory Responses to Continuous and Intermittent Hypoxia Mediated by Hypoxia-Inducible Factors 1 and 2

“…VAH is an important physiological adaptation because failure to hyperventilate at high altitude leads to severe hypoxemia. A large body of evidence suggests that carotid body stimulation and the ensuing chemosensory reflex are critical for evoking VAH (9, 19, 63, 266, 280, 340). …”

Lung disease at high altitude

“…One group of patients at risk for this phenomenon includes those who have undergone unilateral or bilateral carotid endarterectomy (CEA) as impaired HVR has been documented in this population [192,193]. Roeggla et al , for example, examined the effect of moderate altitude (1600 m) on gas exchange in patients before and after unilateral CEA and found that, following surgery, patients developed worse hypoxemia and less hyperventilation when compared with their presurgery baseline [194]. Such problems may not be limited to post-CEA patients.…”