Journal of applied physiology
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In 19 dogs anesthetized with xylazine and alpha-chloralose, we examined the influence of background vagal C-fiber activity on the breathing pattern using a modified perineural capsaicin treatment. In seven dogs, we tested the efficacy of this treatment by recording compound action potentials before and after capsaicin application. In the remaining 12 dogs, we examined the effect of vagal perineural capsaicin on the Hering-Breuer expiratory facilitatory inflation reflex, pulmonary chemoreflex, and breathing pattern (tidal volume and expiratory and inspiratory times). ⋯ The myelinated fiber-initiated Hering-Breuer reflex remained intact after perineural capsaicin, but the C-fiber-initiated pulmonary chemoreflex was abolished. Perineural capsaicin increased tidal volume (0.399 +/- 0.031 to 0.498 +/- 0.058 liter; P < 0.05), expiratory time (3.62 +/- 0.31 to 4.82 +/- 0.68 s; P < 0.05), inspiratory time (1.49 +/- 0.12 to 1.72 +/- 0.17 s; P < 0.10) and total time per breath (5.11 +/- 1.08 to 6.54 +/- 0.82 s; P < 0.05). We conclude that background vagal C-fiber activity exerts an inhibitory effect on tidal volume and an excitatory effect on breathing frequency.
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We have recently observed obstructive apneas during nasal intermittent positive-pressure ventilation (nIPPV) and suggested that they were due to hypocapnia-induced glottic closure. To confirm this hypothesis, we studied seven healthy subjects and submitted them to nIPPV while their glottis was continuously monitored through a fiber-optic bronchoscope. During wakefulness, we measured breath by breath the widest inspiratory angle formed by the vocal cords at the anterior commissure along with several other indexes. ⋯ Moreover, activation of the diaphragmatic muscle was always associated with a significant inspiratory abduction of the vocal cords. Sporadically, complete adduction of the vocal cords was directly responsible for obstructive laryngeal apneas and cyclic changes in the glottic aperture resulted in waxing and waning of tidal volume. We conclude that in awake humans passive ventilation with nIPPV results in vocal cord adduction that depends partly on hypocapnia, but our results suggest that other factors may also influence glottic width.
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Cerebral blood flow (CBF), systemic hemodynamics, and arterial blood gases were measured during control conditions and during and after exposure to either 300 kPa O2 (group 1) or 300 kPa O2 with 2 kPa CO2 (group 2) in awake rats. The respiratory frequency fell with no change of arterial PCO2 (PaCO2) in group 1, but in group 2, respiratory frequency and PaCO2 increased linearly. The cardiac output (CO) and heart rate (HR) fell and systolic arterial pressure (SAP) rose independent of PACO2. ⋯ CBF and rCBF fell despite unaltered PaCO2, whereas hypercapnia prevented these declines. An uneven effect of O2 was observed on rCBF, most pronounced in brain stem regions, independent of the PaCO2. There was a prolonged suppression of O2 supply to brain stem regions both during and after the exposure to O2 in the absence of CO2.
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Clinical Trial
Effect of lung volume on forced expiratory flows during rapid thoracoabdominal compression in infants.
The rapid thoracoabdominal compression (RTC) technique is commonly used in pulmonary function laboratories to assess flow-volume relationships in infants unable to produce a voluntary forced expiration maneuver. This technique produces forced expiratory flows over only a small lung volume segment (i.e., tidal volume). It has been argued that the RTC technique should be modified to measure flow-volume relationships over a larger portion of the vital capacity range to imitate the voluntary maximal forced expiratory maneuver obtained in older children and adults. ⋯ We compared maximal expiratory flows at isovolume points (25 and 10% of forced vital capacity) and found no significant differences in maximal isovolume flow rates measured from the different lung volumes. We conclude that there is no obvious need to initiate RTC from higher lung volumes if the technique is used for flow comparisons. However, compared with measurements of maximal flows at functional residual capacity by RTC from end-tidal inspiration, the initiation of RTC from a defined and reproducible inspiratory level appears to decrease the intrasubject variability of the maximal expiratory flows at low lung volumes.
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To test for an active vasodilator system in human hand and finger skin, seven subjects had a small area of dorsal hand, palm, or dorsal finger pretreated with bretylium (BT) to block adrenergic vasoconstriction. Skin blood flow was monitored at a BT-treated site, a comparable untreated site, and the forearm by laser-Doppler flowmetry. Cutaneous vascular conductance (CVC) was evaluated from the ratio of blood flow to arterial pressure. ⋯ With body heating, increases in CVC at untreated sites of forearm, palm, dorsal hand, and dorsal finger were 881 +/- 165, 779 +/- 368, 423 +/- 115, and 1,430 +/- 716%, respectively (all P < 0.05). At BT-treated sites of palm, dorsal hand, and dorsal finger, increases were 35 +/- 15, 342 +/- 107, and 343 +/- 34%, respectively (palm not significant, others P < 0.05). Increased CVC at the palm began after 1.2 +/- 0.2 min of heating, significantly earlier than forearm (11.8 +/- 2.5 min), dorsal hand (16.4 +/- 3.4 min), or dorsal finger (15.6 +/- 3.6 min), which did not differ significantly from one another.(ABSTRACT TRUNCATED AT 250 WORDS)