Influence of Cold Exposure on Ventilation, Respiratory Heat Loss, and Pulmonary Deposition/Clearance.

摘要

Possible thermoregulatory benefits of cold-induced changes in breathing pattern (hypoventilation) and the mechanism(s) by which cold stimulates a change in breathing pattern were investigated in male Holstein calves 1-3 months old. Effects of ambient temperatures (Ta) between 4 and 18 C on ventilatory parameters and respiratory heat loss were determined in 4 calves. As Ta decreased, respiratory frequency decreased 29% while tidal volume increased 35%. Total ventilation (VE) did not change significantly, but the ventilatory equivalent for O2 decreased with decreasing Ta. Calves were capable of conserving respiratory heat during cold exposure by decreasing expired air temperature and by decreasing dead space ventilation while increasing O2 extraction. hypoventilation is suggested as a mode of heat conservation in cold environments in animals which use panting as a means of increasing evaporative heat loss. The effect of cold-induced hypoventilation on pulmonary particle deposition was investigated in 10 calves. Deposition of nasally-instilled fluorescent Pasteurella haemolytica was significantly higher for cold-exposed calves. It is speculated that the cold-induced respiratory pattern change was responsible. Nasal mucus velocity (NMV) was measured in four unanesthetized calves at Ta = 2-4 C and Ta = 16-18 C, using a radiographic tracking technique. NMV was 24% lower during cold exposure. It is possible that cold-exposure decreases tracheal mucociliary clearance rate. It is speculated that mucociliary clearance rate may be partially genetically determined. Cold-induced decreases in particle clearance, and increases in deposition, may predispose calves to respiratory infection. Keyword: Dissertations. (EDC)