Effects of tension of the girth strap on respiratory system mechanics in horses at rest and during hyperpnea induced by administration of lobeline hydrochloride.
OBJECTIVE
To determine whether tension of the girth strap of a saddle would sufficiently affect rib motion and reduce lung volume to alter pulmonary resistance in horses.


METHODS
10 healthy adult horses.


METHODS
We used classical techniques to measure the effects of tightening a girth strap (15 kg of tension) on pulmonary dynamics during eupnea and hyperpnea in horses. Respiratory impedance was evaluated by use of oscillometry, and resistance and reactance data were partitioned into lung and chest wall components. Rib cage and abdominal contributions to tidal volume and minute ventilation were measured by use of respiratory inductance plethysmography. Effects of strap tension on functional residual capacity (FRC) were measured during eupnea by use of a helium-dilution technique. In a subgroup of 6 horses, we also measured transdiaphragmatic pressures during eupnea and hyperpnea induced by administration of lobeline hydrochloride (0.2 mg/kg, i.v.).


RESULTS
Pulmonary resistance measured by use of oscillometry but not by use of classical methods was significantly increased by the tension of the girth strap. However, the increase in pulmonary resistance could not be explained by a decrease in FRC. Motion of the rib cage was significantly reduced during eupnea and hyperpnea. However, ventilatory variables (tidal volume, minute ventilation, and peak flows), FRC, and transdiaphragmatic pressures were unaltered by strap tension.


CONCLUSIONS
Although tension of the girth strap caused measurable changes in respiratory mechanics (loss of rib motion and increased pulmonary resistance), there was no evidence that ventilation was limited.
Hoffman
Andrew M
AM
Department of Clinical Sciences, Massachusetts School of Veterinary Medicine, Tufts University, North Grafton, MA 01536, USA.
Swanson
Lisa G
LG
Bruns
Susan J
SJ
Kuehn
Heike
H
Bedenice
Daniela
D
D000818:Animals; D003250:Constriction; D006736:Horses / Q000502:physiology*; D008120:Lobeline / Q000494:pharmacology; D011312:Pressure; D012119:Respiration / Q000187:drug effects; D015656:Respiratory Mechanics / Q000187:drug effects / Q000502:physiology*; D019141:Respiratory System Agents / Q000494:pharmacology*
D019141:Respiratory System Agents; D008120:Lobeline