Pm. Heerdt et Be. Pleimann, THE DOSE-DEPENDENT EFFECTS OF HALOTHANE ON RIGHT-VENTRICULAR CONTRACTION PATTERN AND REGIONAL INOTROPY IN SWINE, Anesthesia and analgesia, 82(6), 1996, pp. 1152-1158
The right ventricle (RV) is comprised of two embryo-logically distinct
units, the inflow and outflow tracts, which normally contract sequent
ially and differ in the magnitude of increased inotropy during sympath
etic nervous stimulation. The present study examined the dose-response
effects of halothane on the RV contraction pattern and regional contr
actility in seven open-chest pigs instrumented for measurement of infl
ow and outflow tract pressures and segment lengths. The RV contraction
pattern was evaluated by comparing the phase of inflow and outflow tr
act shortening and regional contractility was determined by calculatio
n of preload recruitable stroke work (PRSW) slope. Using this methodol
ogy, an inflow-outflow tract contraction phase difference of -27 degre
es (inflow tract shortened earlier) was evident at baseline, but was a
bolished by 1.0 and 1.5 minimum alveolar anesthetic concentration (MAC
) halothane; PRSW slope of both the inflow and outflow tracts, however
, demonstrated similar dose-related change. To determine whether alter
ations in cardiac sympathovagal balance Flayed a role in the RV respon
se to halothane, an additional four animals were studied after pretrea
tment with hexamethonium, propranolol, and atropine. In these animals,
there was no difference in the regional contraction phase either at b
aseline or during halothane administration, and dose-related depressio
n of PRSW by halothane was again similar in both regions. However, whe
n halothane effects on regional PRSW in animals with autonomic blockad
e were compared to those of neurally intact animals, a 20% greater dep
ression of outflow tract PRSW by 0.5 MAC halothane was evident. This s
tudy demonstrates that halothane abolishes the normal sequential patte
rn of RV contraction without exerting markedly variant negative inotro
pic effects within different regions of the RV, and provides evidence
to suggest that alterations in cardiac sympathovagal balance may contr
ibute to the effect of halothane on RV contraction dynamics.