HYPOXIC CHEMOSENSITIVITY IN ASTHMATIC-PATIENTS 2 DECADES AFTER CAROTID-BODY RESECTION

Hypoxic chemosensitivity was assessed using 6 methods in 11 patients who had bilateral carotid body resection (termed BR) for asthma 25.1 ± 1.2 (SD) yr ago, 10 with unilateral resection (UR) 21.5 ± 4.2 yr ago, and 5 nonoperated controls (C) approximately matched for age and pulmonary limitation. The following tests were made. 1) Single breath: The difference, ΔVI, in 1/min of the second and third breaths following vital capacity inspirations of 15% CO2 in N2 (test) and 5% CO2 in O2 (control). ΔVI was 2.2 ± 1.4 l/min in BR (P < 0.01), 10.9 ± 7.2 l/min in UR, and 22.5 ± 6.9 l/min in C. 2) Withdrawal: During 15 s after 100% O2 terminates hypercapnic hypoxia (PCO2 = control + 5 Torr, PO2 = 60 Torr), the decrement, ΔVI was 1.3 ± 1.2 l/min in BR (P < 0.01), 2.3 ± 1.8 l/min in UR (P < 0.01), and 3.6 ± 1.4 l/min in C. 3) Progressive hypoxia: Isocapnic ΔVI at PAO2 = 40 Torr, ΔV40 = 0.3 ± 3.0 l/min in BR (NS), 6.0 ± 4.3 l/min in UR, and 17.8 ± 8.2 l/min in C. 4) Steady-state CO2 response slope was increased 21% in C by hypoxia PAO2 = 60 Torr), but unaltered by hypoxia in BR and UR subjects. 5) Breath-holding time was shortened by starting at PAO2 = 70 Torr (vs. 200 Torr, by 7.5 ± 4.6 (SE) s in 12 trials in 4 BR patients (P = 0.05). 6) Doxapram, 0.4 mg/kg iv, increased VI at its peak response by 8.0 ± 7.5 l/min in 4 BR and by 21.0 ± 4.3 in 4 C. Tests 1, 2, and 6 thus disclose possible peripheral chemosensitivity in some BR patients; no response was detected in tests 3-5. Regenerated carotid sinus nerve endings and aortic bodies are possible sites.