Background and AimsStudies assessing hiatal hernia (HH)-related effects on lung volumes derived by body plethysmography are limited. We aimed to evaluate the effect of hernia size on lung volumes (including assessment by body plethysmography) and the relationship to functional capacity, as well as the impact of corrective surgery. MethodsSeventy-three patients (7010 years; 54 female) with large HH [meanstandard deviation, intra-thoracic stomach (ITS) (%): 63 +/- 20%; type III in 65/73] had respiratory function data (spirometry, 73/73; body plethysmography, 64/73; diffusing capacity, 71/73) and underwent HH surgery. Respiratory function was analysed in relation to hernia size (groups I, II and III: 50, 50%-75% and 75% ITS, respectively) and functional capacity. Post-operative changes were quantified in a subgroup. ResultsTotal lung capacity (TLC) and vital capacity (VC) correlated inversely with hernia size (TLC: 97 +/- 11%, 96 +/- 13%, 88 +/- 10% predicted in groups I, II and III, respectively, P=0.01; VC: 110 +/- 17%, 111 +/- 14%, 98 +/- 14% predicted, P=0.02); however, mean values were normal and only 14% had abnormal lung volumes. Surgery increased TLC (93 +/- 11% vs 97 +/- 10% predicted) and VC (105 +/- 15% vs 116 +/- 18%), and decreased residual volume/total lung capacity (RV/TLC) ratio (39 +/- 7% vs 37 +/- 6%) (P<0.01 for all). Respiratory changes were modest relative to the marked functional class improvement. Among parameters that improved following HH surgery, decreased TLC and forced expiratory volume in 1s and increased RV/TLC ratio correlated with poorer functional class pre-operatively. ConclusionsIncreasing HH size correlates with reduced TLC and VC. Surgery improves lung volumes and gas trapping; however, the changes are mild and within the normal range.