Cross, Troy James

Heart failure (HF) is a complex and multifaceted disease. The disease affects multiple organ systems, including the respiratory system. This review provides three unique examples illustrating how the cardiovascular and respiratory systems interrelate because of the pathology of HF. Specifically, these examples outline the impact of HF pathophysiology on 1) respiratory mechanics and the mechanical “cost” of breathing; 2) mechanical interactions of the heart and lungs; and on 3) abnormalities of pulmonary gas exchange during exercise, and how this may be applied to treatment. The goal of this review is to, therefore, raise the awareness that HF, though primarily a disease of the heart, is accompanied by marked pathology of the respiratory system.

The purpose of this report was to 1) detail the construction of a low-cost device that provides a “reference” flow waveform for pneumotachograph (PNT) calibration, i.e., the “syringe potentiometer” (SP), and to compare the 2) accuracy and 3) practical performance of “calibration curves” obtained with the SP device to other more established methods of PNT calibration, i.e., the weighted averaging (WA) and polynomial least-squares (PolyLS) methods. Volume and flow waveforms obtained via the SP device were validated against a motion capture system and were deemed accurate surrogates of actual syringe volume and flows. The SP device was used to construct a calibration curve of a PNT by dividing the flow waveform of the SP by the analog output of the PNT amplifier. A total of 187 inspiratory and 187 expiratory strokes were collected. When the entire data set of expiratory strokes was used, the SP, WA, and PolyLS methods together demonstrated acceptable volume and flow errors as per American Thoracic Society/European Respiratory Society recommendations (less than ±3.5% and less than ±5.0% errors, respectively). The “practical” performance of each method was assessed with a nested subsampling procedure, whereby volume and flow errors were evaluated as the number of strokes was increased (in blocks of 5 strokes). To this end, the SP method demonstrated practical performance superior to that of the WA and PolyLS approaches, whereby acceptable volume and flow errors were achieved after only 5 calibration strokes; the WA and PolyLS methods required 15 and 20 strokes, respectively, to achieve the same level of volume and flow accuracy.NEW & NOTEWORTHY This report describes the construction and validation of a low-cost device for the purposes of pneumotachograph (PNT) calibration: the “syringe potentiometer” (SP). Calibration of a PNT with the SP device yielded acceptable volume and flow errors (<3.5% and 5%, respectively) across a wide range of flows (<0.5 to 15 L/s). The SP device offered superior “practical performance” over other established PNT calibration methods, whereby acceptable volume and flow errors were achieved after only five calibration strokes.

We propose that abnormalities of the pulmonary system contribute significantly to the exertional dyspnea and exercise intolerance observed in patients with chronic heart failure. Interventions designed to address the deleterious pulmonary manifestations of heart failure may, therefore, yield promising improvements in exercise tolerance in this population.

Introduction: Long-term use of continuous-flow left ventricular assist devices may have negative consequences for autonomic, cardiovascular and gastrointestinal function. It has thus been suggested that non-invasive monitoring of arterial pulsatility in patients with a left ventricular assist device is highly important for ensuring patient safety and longevity. We have developed a novel, semi-automated frequency-domain-based index of arterial pulsatility that is obtained during suprasystolic occlusions of the upper arm: the ‘cuff pulsatility index’. Purpose: The purpose of this study was to evaluate the relationship between the cuff pulsatility index and invasively determined arterial pulsatility in patients with a left ventricular assist device. Methods: Twenty-three patients with a left ventricular assist device with end-stage heart failure (six females: age = 65 ± 9 years; body mass index = 30.5 ± 3.7 kg m −2 ) were recruited for this study. Suprasystolic occlusions were performed on the upper arm of the patient’s dominant side, from which the cuff pressure waveform was obtained. Arterial blood pressure was obtained from the radial artery on the contralateral arm. Measurements were obtained in triplicate. The relationship between the cuff pressure and arterial blood pressure waveforms was assessed in the frequency-domain using coherence analysis. A mixed-effects approach was used to assess the relationship between cuff pulsatility index and invasively determined arterial pulsatility (i.e. pulse pressure). Results: The cuff pressure and arterial blood pressure waveforms demonstrated a high coherence up to the fifth harmonic of the cardiac frequency (heart rate). The cuff pulsatility index accurately tracked changes in arterial pulse pressure within a given patient across repeated measurements. Conclusions: The cuff pulsatility index shows promise as a non-invasive index for monitoring residual arterial pulsatility in patients with a left ventricular assist device across time.

Airway luminal area is the major determinant of resistance to airflow in the tracheobronchial tree. Women may have smaller central conducting airways than men; however, previous evidence is confounded by an indirect assessment of airway geometry and by subjects with prior smoking history. The purpose of this study was to examine the effect of sex on airway size in healthy nonsmokers. Using low-dose high-resolution computed tomography, we retrospectively assessed airway luminal area in healthy men ( n = 51) and women ( n = 73) of varying ages (19–86 yr). Subjects with a positive smoking history, cardiopulmonary disease, or a body mass index > 40 kg/m2 were excluded. Luminal areas of the trachea, right and left main bronchus, bronchus intermediate, left and right upper lobes, and the left lower lobe were analyzed at three discrete points. The luminal areas of the conducting airways were ~26%–35% smaller in women. The trachea had the largest differences in luminal area between men and women (298 ± 47 vs. 195 ± 28 mm2 or 35% smaller for men and women, respectively), whereas the left lower lobe had the smallest differences (57 ± 15 vs. 42 ± 9 mm2 or 26% smaller for men and women, respectively). When a subset of subjects was matched for height, the sex differences in airway luminal area persisted, with women being ~20%–30% smaller. With all subjects, there were modest relationships between height and airway luminal area ( r = 0.73–0.53, P < 0.05). Although there was considerable overlap between sexes, the luminal areas of the large conducting airways were smaller in healthy women than in men. NEW & NOTEWORTHY Previous evidence for sex differences in airway size has been confounded by indirect measures and/or cohorts with significant smoking histories or pathologies. We found that central airways in healthy women were significantly smaller (~26%–35%) than men. The significant sex-difference in airway size was attenuated (20%–30% smaller) but preserved in a subset of subjects matched for height. Over a range of ages, healthy women have smaller central airways than men.

It is unknown whether the greater total work of breathing (WOB) with aging is due to greater elastic and/or resistive WOB. We hypothesized that older compared with younger adults would exhibit a greater total WOB at matched ventilations (V̇e) during graded exercise, secondary to greater inspiratory resistive and elastic as well as expiratory resistive WOB. Older (OA: 60 ± 8 yr; n = 9) and younger (YA: 38 ± 7 yr; n = 9) adults performed an incremental cycling test to volitional fatigue. Esophageal pressure, inspiratory (IRV) and expiratory reserve volumes (ERV), expiratory flow limitation (EFL), and ventilatory variables were measured at matched V̇e (i.e., 25, 50, and 75 l/min) during exercise. The inspiratory resistive and elastic as well as expiratory resistive WOB were quantified using the Otis method. At V̇e of 75 l/min, older adults had greater %EFL and larger tidal volumes to inspiratory capacity but smaller relative IRV ( P ≤ 0.03) than younger adults. Older compared with younger adults had greater total WOB at V̇Eof 50 and 75 l/min (OA: 90 ± 43 vs. YA: 49 ± 21 J/min; P < 0.04 for both). At V̇e of 75 l/min, older adults had greater inspiratory elastic and resistive WOB (OA: 44 ± 27 vs. YA: 24 ± 22 and OA: 23 ± 15 vs. YA: 11 ± 3 J/min, respectively, P < 0.03 for both) and expiratory resistive WOB (OA: 23 ± 19 vs. YA: 14 ± 9 J/min, P = 0.02) than younger adults. These data demonstrate that aging-induced pulmonary alterations result in greater inspiratory elastic and resistive as well as expiratory resistive WOB, which may have implications for the integrated response during exercise.NEW & NOTEWORTHY Aging-induced changes to the pulmonary system result in increased work of breathing (WOB) during exercise. However, it is not known whether this higher WOB with aging is due to differences in elastic and/or resistive WOB. Herein, we demonstrate that older adults exhibited greater inspiratory elastic and resistive as well as expiratory resistive WOB during exercise.

Chest wall strapping has been used to assess mechanisms of dyspnea with restrictive lung disease. This study examined the hypothesis that dyspnea with restriction depends principally on the degree of reflex ventilatory stimulation. We compared dyspnea at the same (iso)ventilation when added dead space provided a component of the ventilatory stimulus during exercise. Eleven healthy men undertook a randomized controlled crossover trial that compared four constant work exercise conditions: 1) control (CTRL): unrestricted breathing at 90% gas exchange threshold (GET); 2) CTRL+dead space (DS): unrestricted breathing with 0.6-l dead space, at isoventilation to CTRL due to reduced exercise intensity; 3) CWS: chest wall strapping at 90% GET; and 4) CWS+DS: chest strapping with 0.6-l dead space, at isoventilation to CWS with reduced exercise intensity. Chest strapping reduced forced vital capacity by 30.4 ± 2.2% (mean ± SE). Dyspnea at isoventilation was unchanged with CTRL+DS compared with CTRL (1.93 ± 0.49 and 2.17 ± 0.43, 0–10 numeric rating scale, respectively; P = 0.244). Dyspnea was lower with CWS+DS compared with CWS (3.40 ± 0.52 and 4.51 ± 0.53, respectively; P = 0.003). Perceived leg fatigue was reduced with CTRL+DS compared with CTRL (2.36 ± 0.48 and 2.86 ± 0.59, respectively; P = 0.049) and lower with CWS+DS compared with CWS (1.86 ± 0.30 and 4.00 ± 0.79, respectively; P = 0.006). With unrestricted breathing, dead space did not change dyspnea at isoventilation, suggesting that dyspnea does not depend on the mode of reflex ventilatory stimulation in healthy individuals. With chest strapping, dead space presented a less potent stimulus to dyspnea, raising the possibility that leg muscle work contributes to dyspnea perception independent of the ventilatory stimulus. NEW & NOTEWORTHY Chest wall strapping was applied to healthy humans to simulate restrictive lung disease. With chest wall strapping, dyspnea was reduced when dead space substituted for part of a constant exercise stimulus to ventilation. Dyspnea associated with chest wall strapping depended on the contribution of leg muscle work to ventilatory stimulation. Chest wall strapping might not be a clinically relevant model to determine whether an alternative reflex ventilatory stimulus mimics the intensity of exertional dyspnea.

It is generally recommended that an esophageal balloon-catheter possess an adequate frequency response up to 15 Hz, such that parameters of respiratory mechanics may be quantified with precision. In our experience, however, we have observed that some commercially available systems do not display an ideal frequency response (<8-10 Hz). We therefore investigated whether the poor frequency response of a commercially available esophageal catheter may be adequately compensated using two numerical techniques: 1) an exponential model correction, and 2) Wiener deconvolution. These two numerical techniques were performed on a commercial balloon-catheter interfaced with 0, 1, and 2 lengths of extension tubing (90 cm each), referred to as configurations L0, L90, and L180, respectively. The frequency response of the balloon-catheter in these configurations was assessed by empirical transfer function analysis, and its “working” range was defined as the frequency beyond which more than 5% amplitude and/or phase distortion was observed. The working frequency range of the uncorrected balloon-catheter extended up to only 10 Hz for L0, and progressively worsened with additional tubing length (L90 = 3 Hz, L180 = 2 Hz). Although both numerical methods of correction adequately enhanced the working frequency range of the balloon-catheter to beyond 25 Hz for all length configurations (L0, L90, and L180), Wiener deconvolution consistently provided more accurate corrections. Our data indicate that Wiener deconvolution provides a superior correction of the balloon-catheter's dynamic response, and is relatively more robust to extensions in catheter tube length compared with the exponential correction method.

SummaryThe purpose of this study was to examine the effect of venous occlusion per se on forearm muscle blood flow, as determined by the near‐infrared spectroscopy (NIRS) venous occlusion technique (NIRS‐VOT). NIRS data were obtained from the flexor digitorum superficialis (FDS) muscle on the dominant arm of 16 young, ostensibly healthy participants (14 men and two women; 30 ± 6 year; 73 ± 7 kg). Participants completed a series of five venous occlusion trials while seated at rest, and a series of 12 venous occlusion trials during a reactive hyperaemia induced by 5 min of forearm arterial occlusion. The NIRS‐VOT was used to assess FDS muscle blood flow (), beat‐by‐beat, over the first four cardiac beats during venous occlusions. was also reported as a cumulative value, wherein the first two, first three and first four cardiac beats were used to calculate muscle blood flow. We observed that was highest when calculated over the first cardiac beat during venous occlusions performed at rest and throughout reactive hyperaemia (P<0·05). Moreover, the inclusion of more than one cardiac beat in the calculation of underestimated muscle blood flows, irrespective of the prevailing level of arterial inflow. These findings support the idea that venous occlusion per se affects the measurement of via the NIRS‐VOT. Accordingly, it is recommended that is determined over the first cardiac beat when using the NIRS‐VOT to assess microvascular blood flow of human forearm muscles.