Fick principle and exercise pulmonary hemodynamic determinants of the six‐minute walk distance in pulmonary hypertension

Abstract

The six-minute walk test is widely used to assess the severity and prognosis of pulmonary hypertension. However, the pathophysiology underlying a compromised six-minute walk distance is incompletely characterized. The purpose of this study is to evaluate the Fick principle and pulmonary hemodynamic determinants of the six-minute walk distance in patients with suspected pulmonary hypertension. Twenty-nine patients were retrospectively studied and underwent a right heart catheterization for the evaluation of suspected pulmonary hypertension. With the pulmonary artery catheter in place, patients were moved to a treadmill and completed a six-minute walk test. Fick cardiac output and indices of right heart afterload were calculated using continuous measurements of pulmonary vascular pressures, gas exchange, and mixed venous blood samples. Fifteen subjects who walked ≤ 348 m were compared to 14 subjects who walked > 348 m. Systemic oxygen delivery was impaired in six-minute walk distance ≤ 348 m compared to six-minute walk distance > 348 m (15.2 ± 6.2 vs. 23.2 ± 6.8 mL/kg/min, p < 0.01). Impaired oxygen delivery was due to a depressed cardiac index and decreased cardiac reserve demonstrated by the change in the stroke volume index (3.0 ± 14 vs. 17 ± 15 mL/min/m2, p = 0.02). The six-minute walk distance positively correlated with oxygen delivery ( r = 0.501, p = 0.006) and inversely correlated with oxygen extraction ( r = 0.369, p = 0.049). A decreased six-minute walk distance was associated with an increased total pulmonary resistance ( r = 0.502, p = 0.006) and pulmonary vascular resistance ( r = 0.530, p = 0.003). In patients with suspected pulmonary hypertension, a decreased six-minute walk distance is due to compromised oxygen delivery, decreased cardiac reserve, and increased right ventricular afterload.

Noninvasive determinants of pulmonary hypertension in interstitial lung disease

“…In the current study, PH‐ILD patients exhibited lower 6MWD along with greater systemic O 2 desaturation compared to ILD patients without PH. However, a change in 6MWD in PH‐ILD is nonspecific and can reflect worsening parenchymal lung disease, a pulmonary vascular process, and also a range of other pathologies including individual biomechanics 8 . Furthermore, in the current study, on ROC analysis, 6MWD provided less discrimination in predicting presence of PH compared to other noninvasive variables (Figure 2).…”

“…Current, commonly employed noninvasive methods used to screen ILD patients for the presence of PH include blood testing for trends in plasma N‐terminal (NT)‐prohormone‐brain natriuretic peptide (NT‐proBNP), transthoracic echocardiography (TTE), worsening pulmonary function test (PFT) parameters, and reduced 6‐min walk distance (6MWD). 6 Unfortunately, these investigative tests in isolation have inherent limitations as a screening tool for PH‐ILD 7 , 8 , 9 and currently there remains no standard approach to assessing patients' risk for PH in ILD. 6 Variations in PH‐ILD screening practices could translate into infrequent patient assessment and potentially delayed diagnosis of PH in the ILD population.…”

The comparative effects of sacubitril/valsartan versus enalapril on pulmonary hypertension due to heart failure with a reduced ejection fraction

“…18 In patients with suspected PH, a decreased 6-min walk distance is due to compromised oxygen delivery, decreased cardiac reserve, and increased RV afterload. 18 In this study, the value of PA/AO in the sacubitril/valsartan group significantly decreased than that in the enalapril group. PA/AO and TAPSE can be used to assess the level of the heart and great vessels without the severity of the shunt in patients with PH.…”

“…The 6-min walk test is widely used to assess the severity and prognosis of PH. 18 In patients with suspected PH, a decreased 6-min walk distance is due to compromised oxygen delivery, decreased cardiac reserve, and increased RV afterload. 18 In this study, the value of PA/AO in the sacubitril/valsartan group significantly decreased than that in the enalapril group.…”

“…There were no significant differences in the use of diuretics, digitalis, and nitrates between the two groups (Table 1). The 6‐min walk test is widely used to assess the severity and prognosis of PH 18 . In patients with suspected PH, a decreased 6‐min walk distance is due to compromised oxygen delivery, decreased cardiac reserve, and increased RV afterload 18 .…”