Effect of circulatory congestion on the components of pulmonary diffusing capacity in morbid obesity.
OBJECTIVE
Obese patients without clinically apparent heart disease may have a high output state and elevated total and central blood volumes. Central circulatory congestion should result in elevated pulmonary diffusing capacity (DLCO) and capillary blood volume (Vc) reflecting pulmonary capillary recruitment; however, the effect on membrane diffusion (Dm) is uncertain. We examined DLCO and its partition into Vc and Dm in 13 severely obese subjects (BMI = 51 +/- 14 kg/m2) without manifest cardiopulmonary disease before and after surgically induced weight loss.


METHODS
DLCO and its partition into Vc and Dm [referenced to alveolar volume (VA)] as described by Roughton and Forster, total body water by tritiated water, and fat distribution by waist-to-hip ratio were performed.


RESULTS
Despite normal DLCO (mean 98 +/- 16% predicted), Vc/VA was increased (mean 118 +/- 30% predicted), and Dm/VA was reduced (mean 77 +/- 34% predicted). Nine of 13 subjects were restudied after weight loss (mean 52 +/- 43 kg); Vc/VA decreased to 89 +/- 18% predicted (p = 0.01), and Dm/VA increased to 139 +/- 30% predicted (p < 0.01). Increasing total body water was associated with both increasing Vc (r = 0.74, p = 0.01) and increasing waist-to-hip ratio (r = 0.65, p = 0.02), indicating that circulatory congestion increases with increasing central obesity.


CONCLUSIONS
Severely obese subjects without manifest cardiopulmonary disease may have increased Vc indicating central circulatory congestion and reduced Dm suggesting associated alveolar capillary leak, despite normal DLCO. Reversibility with weight loss is in accord with reversibility of the hemodynamic abnormalities of obesity.
Oppenheimer
Beno W
BW
Division of Pulmonary and Critical Care Medicine and Bellevue Hospital Chest Service, Department of Medicine, New York University School of Medicine, New York, NY 10016, USA. beno.oppenheimer@med.nyu.edu
Berger
Kenneth I
KI
Rennert
Douglas A
DA
Pierson
Richard N
RN
Norman
Robert G
RG
Rapoport
David M
DM
Kral
John G
JG
Goldring
Roberta M
RM
D000293:Adolescent; D000328:Adult; D001784:Blood Gas Analysis; D001810:Blood Volume / Q000502:physiology*; D001834:Body Water / Q000378:metabolism; D002199:Capillary Permeability / Q000502:physiology*; D005260:Female; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D009767:Obesity, Morbid / Q000503:physiopathology* / Q000601:surgery; D011652:Pulmonary Circulation; D011653:Pulmonary Diffusing Capacity / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012119:Respiration; D012129:Respiratory Function Tests; D014655:Vascular Resistance; D049629:Waist-Hip Ratio; D015431:Weight Loss / Q000502:physiology*