DOES PARALLEL CONDUCTANCE VARY DURING SYSTOLE IN THE HUMAN RIGHT VENTRICLE

Objectives: Right ventricular (RV) contractile performance remains poo rly characterised, particularly in humans, Conductance catheter techni ques have the potential to overcome the geometric difficulties in RV v olume measurement that have hindered systematic studies of RV pressure volume relations. The present study examines changes in parallel cond uctance (Vc) that may occur during the cardiac cycle in the human righ t ventricle. Methods: Using signals obtained from custom-built conduct ance catheters, six isochronal systolic values of Vc (Vc(t)) were meas ured during hypertonic saline wash-in. Studies were performed in nine patients undergoing right heart catheterisation. Their ages ranged fro m 7 to 39 years (median = 16) and their weights ranged from 20.3 to 84 .7 kg (median = 50.0 kg). Measurements of mean Vc and isochronal (<(Vc (t))over bar>) and its variability during systole were assessed. Mean Vc was measured using the Baan technique (Vc(Baan)), (<(Vc(t))over bar >) was measured from six systolic isochrones obtained during the same period of hypertonic saline wash-in. Results: The temporal changes in <(Vc(t))over bar>) were small (mean 5.8%, median = 4.4%, range = 0.6-1 7.9%) of total corrected end-diastolic volume (mean maximal variation of 7.7 mi), The value of <(Vc(t))over bar>) obtained at dp/dt(max) (me an = 99.1 ml; median = 104.75 ml; range 20.15-196.7 ml) was not signif icantly different to that obtained at dp/dt(max) (mean = 100.0 ml, med ian = 110.87 ml, range = 20.0-204.2 ml) (P > 0.05), but both were high er than the single Vc measurement (Vc(Baan)) obtained using the standa rd approach (P = 0.02). The correlation between Vc(Baan) and Vc(t) for group data; (Vc(Baan)= 89.69 ml, s,d. = 43.73 ml; <(Vc(t))over bar>) = 98.16 mi, s.d, = 50.16 ml) produces a regression slope of 0.99 for a ll studies (P = 0.02). Conclusion: We conclude that parallel conductan ce does vary during systole in the human right ventricle of adults and older children after repair of congenital abnormalities but there is no significant difference in <(Vc(t))over bar>) at dp/dt(min), and dp/ dt(max). However, there was a significant difference when the isochron al <(Vc(t))over bar>) measurement is compared with the standard single value technique (Vc(Baan)) obtained using the hypertonic saline wash- in method. The excellent correlation between (<(Vc(t))over bar>) and V c(Baan) suggests that the correction of Vc for the phase of the cardia c cycle is unnecessary for most purposes when studying the human right ventricle.