Pulmonary diffusing capacity for nitric oxide during exercise in morbid obesity

Right ventricular-pulmonary arterial coupling impairment and exercise capacity in obese adults

Background

Obesity-related exercise intolerance may be associated with pulmonary vascular and right ventricular dysfunction. This study tested the hypothesis that decreased pulmonary vascular reserve and right ventricular (RV)-pulmonary arterial (PA) uncoupling contributes to exercise limitation in subjects with obesity.

Methods

Seventeen subjects with obesity were matched to normo-weighted healthy controls. All subjects underwent; exercise echocardiography, lung diffusing capacity (DL) for nitric oxide (NO) and carbon monoxide (CO) and an incremental cardiopulmonary exercise test. Cardiac output (Q), PA pressure (PAP) and tricuspid annular plane systolic excursion (TAPSE) were recorded at increasing exercise intensities. Pulmonary vascular reserve was assessed by multipoint mean PAP (mPAP)/Q relationships with more reserve defined by lesser increase in mPAP at increased Q, and RV-PA coupling was assessed by the TAPSE/systolic PAP (sPAP) ratio.

Results

At rest, subjects with obesity displayed lower TAPSE/sPAP ratios (1.00 ± 0.26 vs. 1.19 ± 0.22 ml/mmHg, P < 0.05), DLCO and pulmonary capillary blood volume (52 ± 11 vs. 64 ± 13 ml, P < 0.01) compared to controls. Exercise was associated with steeper mPAP-Q slopes, decreased TAPSE/sPAP and lower peak O2 uptake (VO2peak). The changes in TAPSE/sPAP at exercise were correlated to the body fat mass (R = 0.39, P = 0.01) and VO2peak (R = 0.44, P < 0.01).

Conclusion

Obesity is associated with a decreased pulmonary vascular and RV-PA coupling reserve which may impair exercise capacity.

Test-retest reliability of lung diffusing capacity for nitric oxide during light to moderate intensity cycling exercise

This study examined test-retest reliability of single-breath lung diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) during exercise. Sixteen healthy subjects (age 20-67 years) performed DLNO-DLCO tests during light and moderate intensity cycling exercise at 50% and 80% of individual anaerobic threshold (IAT). Primary endpoint was DLNO at 80% IAT. Precision of DLNO, DLCO, and alveolar volume was quantified by within-subject standard deviation (SD_ws, measurement error) and intraclass correlation coefficients (ICC). Reproducibility was determined by SD_ws* 2.77. Overall, reliability was excellent for all outcomes. SD_ws and reproducibility for DLNO at 80% IAT were 4.6 and 12.7 mL.min^-1.mmHg^-1, and the ICC was 0.99 (95% confidence interval 0.98-0.99). Median breathlessness at 80% IAT was 4 (interquartile range 3-6) on a 0-10 scale. Our data suggest excellent reliability of single-breath DLNO during moderate intensity exercise, but perceived levels of breathlessness may limit its usefulness, especially at exercise intensities beyond IAT.

The association between transfer coefficient of the lung and the risk of exacerbation in asthma-COPD overlap: an observational cohort study

BACKGROUND

Asthma-chronic obstructive pulmonary disease (COPD) overlap (ACO) patients experience exacerbations more frequently than those with asthma or COPD alone. Since low diffusing capacity of the lung for carbon monoxide (DLCO) is known as a strong risk factor for severe exacerbation in COPD, DLCO or a transfer coefficient of the lung for carbon monoxide (KCO) is speculated to also be associated with the risk of exacerbations in ACO.

METHODS

This study was conducted as an observational cohort survey at the National Hospital Organization Fukuoka National Hospital. DLCO and KCO were measured in 94 patients aged ≥ 40 years with a confirmed diagnosis of ACO. Multivariable-adjusted hazard ratios (HRs) for the exacerbation-free rate over one year were estimated and compared across the levels of DLCO and KCO.

RESULTS

Within one year, 33.3% of the cohort experienced exacerbations. After adjustment for potential confounders, low KCO (< 80% per predicted) was positively associated with the incidence of exacerbation (multivariable-adjusted HR = 3.71 (95% confidence interval 1.32-10.4)). The association between low DLCO (< 80% per predicted) and exacerbations showed similar trends, although it failed to reach statistical significance (multivariable-adjusted HR = 1.31 (95% confidence interval 0.55-3.11)).

CONCLUSIONS

Low KCO was a significant risk factor for exacerbations among patients with ACO. Clinicians should be aware that ACO patients with impaired KCO are at increased risk of exacerbations and that careful management in such a population is mandatory.

Lung function and breathing patterns in hospitalised COVID-19 survivors: a review of post-COVID-19 Clinics

INTRODUCTION

There is relatively little published on the effects of COVID-19 on respiratory physiology, particularly breathing patterns. We sought to determine if there were lasting detrimental effect following hospital discharge and if these related to the severity of COVID-19.

METHODS

We reviewed lung function and breathing patterns in COVID-19 survivors > 3 months after discharge, comparing patients who had been admitted to the intensive therapy unit (ITU) (n = 47) to those who just received ward treatments (n = 45). Lung function included spirometry and gas transfer and breathing patterns were measured with structured light plethysmography. Continuous data were compared with an independent t-test or Mann Whitney-U test (depending on distribution) and nominal data were compared using a Fisher's exact test (for 2 categories in 2 groups) or a chi-squared test (for > 2 categories in 2 groups). A p-value of < 0.05 was taken to be statistically significant.

RESULTS

We found evidence of pulmonary restriction (reduced vital capacity and/or alveolar volume) in 65.4% of all patients. 36.1% of all patients has a reduced transfer factor (TLCO) but the majority of these (78.1%) had a preserved/increased transfer coefficient (KCO), suggesting an extrapulmonary cause. There were no major differences between ITU and ward lung function, although KCO alone was higher in the ITU patients (p = 0.03). This could be explained partly by obesity, respiratory muscle fatigue, localised microvascular changes, or haemosiderosis from lung damage. Abnormal breathing patterns were observed in 18.8% of subjects, although no consistent pattern of breathing pattern abnormalities was evident.

CONCLUSIONS

An "extrapulmonary restrictive" like pattern appears to be a common phenomenon in previously admitted COVID-19 survivors. Whilst the cause of this is not clear, the effects seem to be similar on patients whether or not they received mechanical ventilation or had ward based respiratory support/supplemental oxygen.

Simultaneous measurement of pulmonary diffusing capacity for carbon monoxide and nitric oxide

In Europe and America, the newly-developed, simultaneous measurement of diffusing capacity for CO (DLCO) and NO (DLNO) has replaced the classic DLCO measurement for detecting the pathophysiological abnormalities in the acinar regions. However, simultaneous measurement of DLCO and DLNO is currently not used by Japanese physicians. To encourage the use of DLNO in Japan, the authors reviewed aspects of simultaneously-estimated DLCO and DLNO from previously published manuscripts. The simultaneous DLCO-DLNO technique identifies the alveolocapillary membrane-related diffusing capacity (membrane component, DM) and the blood volume in pulmonary microcirculation (VC); VC is the principal factor constituting the blood component of diffusing capacity (DB,DB=θ·VC where θ is the specific gas conductance for CO or NO in the blood). As the association velocity of NO with hemoglobin (Hb) is fast and the affinity of NO with Hb is high in comparison with those of CO, θNO can be taken as an invariable simply determined by diffusion limitation inside the erythrocyte. This means that θNO is independent of the partial pressure of oxygen (PO2). However, θCO involves the limitations by diffusion and chemical reaction elicited by the erythrocyte, resulting in θCO to be a PO2-dependent variable. Furthermore, DLCO is determined primarily by DB (∼77%), while DLNO is determined equally by DM (∼55%) and DB (∼45%). This suggests that DLCO is more sensitive for detecting microvascular diseases, while DLNO can equally identify alveolocapillary membrane and microcirculatory abnormalities.

Standardisation and application of the single-breath determination of nitric oxide uptake in the lung

Diffusing capacity of the lung for nitric oxide (D_LNO), otherwise known as the transfer factor, was first measured in 1983. This document standardises the technique and application of single-breath D_LNO This panel agrees that 1) pulmonary function systems should allow for mixing and measurement of both nitric oxide (NO) and carbon monoxide (CO) gases directly from an inspiratory reservoir just before use, with expired concentrations measured from an alveolar "collection" or continuously sampled via rapid gas analysers; 2) breath-hold time should be 10 s with chemiluminescence NO analysers, or 4-6 s to accommodate the smaller detection range of the NO electrochemical cell; 3) inspired NO and oxygen concentrations should be 40-60 ppm and close to 21%, respectively; 4) the alveolar oxygen tension (P_AO2 ) should be measured by sampling the expired gas; 5) a finite specific conductance in the blood for NO (θNO) should be assumed as 4.5 mL·min^-1·mmHg^-1·mL^-1 of blood; 6) the equation for 1/θCO should be (0.0062·P_AO2 +1.16)·(ideal haemoglobin/measured haemoglobin) based on breath-holding P_AO2 and adjusted to an average haemoglobin concentration (male 14.6 g·dL^-1, female 13.4 g·dL^-1); 7) a membrane diffusing capacity ratio (D_MNO/D_MCO) should be 1.97, based on tissue diffusivity.

TheTL,NO/TL,COratio in pulmonary function test interpretation

The transfer factor of the lung for nitric oxide (TL,NO) is a new test for pulmonary gas exchange. The procedure is similar to the already well-established transfer factor of the lung for carbon monoxide (TL,CO). Physiologically,TL,NOpredominantly measures the diffusion pathway from the alveoli to capillary plasma. In the Roughton–Forster equation,TL,NOacts as a surrogate for the membrane diffusing capacity (DM). The red blood cell resistance to carbon monoxide uptake accounts for ∼50% of the total resistance from gas to blood, but it is much less for nitric oxide.

TL,NOandTL,COcan be measured simultaneously with the single breath technique, andDMand pulmonary capillary blood volume (Vc) can be estimated.TL,NO, unlikeTL,CO, is independent of oxygen tension and haematocrit. TheTL,NO/TL,COratio is weighted towards theDM/Vcratio and to α; where α is the ratio of physical diffusivities of NO to CO (α=1.97). TheTL,NO/TL,COratio is increased in heavy smokers, with and without computed tomography evidence of emphysema, and reduced in the voluntary restriction of lung expansion; it is expected to be reduced in chronic heart failure. TheTL,NO/TL,COratio is a new index of gas exchange that may, more than derivations from them ofDMandVcwith their in-built assumptions, give additional insights into pulmonary pathology.

Impact of altered alveolar volume on the diffusing capacity of the lung for carbon monoxide in obesity

BACKGROUND

Studies on the diffusing capacity of the lung for carbon monoxide (DL(CO)) in obese patients are conflicting, some studies showing increased DL(CO) and others unaltered or reduced values in these subjects.

OBJECTIVES

To compare obese patients to controls, examine the contribution of alveolar volume (VA) and CO transfer coefficient (K(CO)) to DL(CO), and calculate DL(CO) values adjusted for VA.

METHODS

We measured body mass index (BMI), waist circumference (WC), spirometry and DL(CO) in 98 adult obese patients without cardiopulmonary or smoking history and 48 healthy subjects. All tests were performed in the same laboratory.

RESULTS

Using conventional reference values, mean DL(CO) and VA were lower (-6%, p < 0.05, and -13%, p < 0.001, respectively), and K(CO) was higher (+9%, p < 0.05) in obese patients than in controls. VA decreased whereas K(CO) increased with increasing BMI and WC in the obese group. Patients with lower DL(CO) had low K(CO) in addition to decreased VA. In contrast, some obese patients maintained normal VA, which, coupled with high K(CO), resulted in higher DL(CO). The main result is that diffusion capacity differences between obese patients and controls disappeared using reference equations adjusting DL(CO) for VA.

CONCLUSIONS

Using conventional reference equations, our obese patients show slightly lower mean DL(CO,) lower mean VA and higher mean K(CO) than controls, but with a large range of DL(CO) values and patterns. Adjusting DL(CO) for VA suggests that low lung volumes are the main cause of low DL(CO) and high K(CO) values in obese patients.