American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Jul 1994
Cardiovascular effects of periodic obstructive and central apneas in dogs.
Patients with sleep apnea may experience two types of apnea, central and obstructive. We compared cardiovascular effects of these two types of apnea matched for changes in arterial blood gas tensions and periodicity. In 12 anesthetized, closed chest dogs, obstructive apneas were induced by completely occluding the endotracheal tube at end-expiration for 1 min and allowing 1 min of spontaneous ventilation. ⋯ During obstructive apneas, right atrial pressure increased, as did right heart blood volume. During central apneas, both right atrial pressure and left atrial pressure increased, as did pulmonary blood volume. We conclude that: (1) HR decreases are more severe during central apnea, most likely due to lack of respiratory mechanoreceptor input; (2) CO decreases more with central compared with obstructive apnea due to the heart rate response; (3) HR-induced cardiac dysfunction with central apnea could lead to pulmonary vascular congestion.
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Previous studies of grain elevator workers have shown exposure-related increased rates for respiratory symptoms and reduced levels of lung function compared with those of other employed populations. However, some reports have suggested that this effect may be reversible after cessation of exposure. To investigate this, we conducted a respiratory health survey among 75 retired grain elevator workers and 37 retired civic workers. ⋯ Grain elevator retirees reported more dyspnea (44 versus 11%, p < 0.01) and had significantly lower levels for both FEV1 (78.6 versus 88.2% pred) and FVC (90.0 versus 97.7% pred) (both p < 0.05). Compared with civic retirees, grain retirees reported the same average level of breathlessness after the 6-min walk test, but they walked a significantly shorter distance (p < 0.01); they also scored higher on the impairment of activities scale and had a greater proportion of persons reporting impairment of daily activities caused by breathing trouble (p < 0.05). Comparison of the changes in lung function from 1975 to the present study (i.e., from active employment to retirement) showed that grain workers had consistently lower levels of lung function than did civic workers while still employed, with no reversibility after retirement.(ABSTRACT TRUNCATED AT 250 WORDS)