Assessing the pulmonary vascular responsiveness to oxygen with proton MRI.

Ventilation-perfusion matching occurs passively and is also actively regulated through hypoxic pulmonary vasoconstriction (HPV). The extent of HPV activity in humans, particularly normal subjects, is uncertain. Current evaluation of HPV assesses changes in ventilation-perfusion relationships/pulmonary vascular resistance with hypoxia and is invasive, or unsuitable for patients because of safety concerns.

The spatial-temporal dynamics of pulmonary blood flow are altered in pulmonary arterial hypertension.

Global fluctuation dispersion (FDglobal), a spatial-temporal metric derived from serial images of the pulmonary perfusion obtained with MRI-arterial spin labeling, describes temporal fluctuations in the spatial distribution of perfusion. In healthy subjects, FDglobal is increased by hyperoxia, hypoxia, and inhaled nitric oxide. We evaluated patients with pulmonary arterial hypertension (PAH, 4F, aged 47 ± 15, mean pulmonary artery pressure 48 ± 7 mmHg) and healthy controls (CON, 7F, aged 47 ± 12) to test the hypothesis that FDglobal is increased in PAH.

Face Masks and the Cardiorespiratory Response to Physical Activity in Health and Disease.

To minimize transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the novel coronavirus responsible for coronavirus disease (COVID-19), the U.S. Centers for Disease Control and Prevention and the World Health Organization recommend wearing face masks in public.

Quantitative Mapping of Specific Ventilation in the Human Lung using Proton Magnetic Resonance Imaging and Oxygen as a Contrast Agent.

Specific ventilation imaging (SVI) is a functional magnetic resonance imaging technique capable of quantifying specific ventilation - the ratio of the fresh gas entering a lung region divided by the region's end-expiratory volume - in the human lung, using only inhaled oxygen as a contrast agent. Regional quantification of specific ventilation has the potential to help identify areas of pathologic lung function. Oxygen in solution in tissue shortens the tissue's longitudinal relaxation time (T1), and thus a change in tissue oxygenation can be detected as a change in T1-weighted signal with an inversion recovery acquired image.

Regional pulmonary perfusion patterns in humans are not significantly altered by inspiratory hypercapnia.

Pulmonary vascular tone is known to be sensitive to both local alveolar Po and Pco. Although the effects of hypoxia are well studied, the hypercapnic response is relatively less understood. We assessed changes in regional pulmonary blood flow in humans in response to hypercapnia using previously developed MRI techniques.

Comparison of quantitative multiple-breath specific ventilation imaging using colocalized 2D oxygen-enhanced MRI and hyperpolarized He MRI.

Two magnetic resonance specific ventilation imaging (SVI) techniques, namely, oxygen-enhanced proton (OE-H) and hyperpolarized He (HP-He), were compared in eight healthy supine subjects [age 32 (6) yr]. An in-house radio frequency coil array for H configured with the He transmit-receive coil in situ enabled acquisition of SVI data from two nuclei from the same slice without repositioning the subjects. After 3 × 3 voxel downsampling to account for spatial registration errors between the two SV images, the voxel-by-voxel correlation coefficient of two SV maps ranged from 0.

Evidence from high-altitude acclimatization for an integrated cerebrovascular and ventilatory hypercapnic response but different responses to hypoxia.

Ventilation and cerebral blood flow (CBF) are both sensitive to hypoxia and hypercapnia. To compare chemosensitivity in these two systems, we made simultaneous measurements of ventilatory and cerebrovascular responses to hypoxia and hypercapnia in 35 normal human subjects before and after acclimatization to hypoxia. Ventilation and CBF were measured during stepwise changes in isocapnic hypoxia and iso-oxic hypercapnia.

Measurement of the distribution of ventilation-perfusion ratios in the human lung with proton MRI: comparison with the multiple inert-gas elimination technique.

We have developed a novel functional proton magnetic resonance imaging (MRI) technique to measure regional ventilation-perfusion (V̇/Q̇) ratio in the lung. We conducted a comparison study of this technique in healthy subjects ( = 7, age = 42 ± 16 yr, Forced expiratory volume in 1 s = 94% predicted), by comparing data measured using MRI to that obtained from the multiple inert gas elimination technique (MIGET). Regional ventilation measured in a sagittal lung slice using Specific Ventilation Imaging was combined with proton density measured using a fast gradient-echo sequence to calculate regional alveolar ventilation, registered with perfusion images acquired using arterial spin labeling, and divided on a voxel-by-voxel basis to obtain regional V̇/Q̇ ratio.

Regional Ventilation Is the Main Determinant of Alveolar Deposition of Coarse Particles in the Supine Healthy Human Lung During Tidal Breathing.

Background: To quantify the relationship between regional lung ventilation and coarse aerosol deposition in the supine healthy human lung, we used oxygen-enhanced magnetic resonance imaging and planar gamma scintigraphy in seven subjects.

Methods: Regional ventilation was measured in the supine posture in a 15 mm sagittal slice of the right lung. Deposition was measured by using planar gamma scintigraphy (coronal scans, 40 cm FOV) immediately postdeposition, 1 hour 30 minutes and 22 hours after deposition of Tc-labeled particles (4.

Rapid Prototyping of Inspired Gas Delivery System for Pulmonary MRI Research.

Specific ventilation imaging (SVI) is a noninvasive magnetic resonance imaging (MRI)-based method for determining the regional distribution of inspired air in the lungs, useful for the assessment of pulmonary function in medical research. This technique works by monitoring the rate of magnetic resonance signal change in response to a series of imposed step changes in inspired oxygen concentration. The current SVI technique requires a complex system of tubes, valves, and electronics that are used to supply and rapidly switch inspired gases while subjects are imaged, which makes the technique difficult to translate into the clinical setting.

The effect of lung deformation on the spatial distribution of pulmonary blood flow.

Key Points: Pulmonary perfusion measurement using magnetic resonance imaging combined with deformable image registration enabled us to quantify the change in the spatial distribution of pulmonary perfusion at different lung volumes. The current study elucidated the effects of tidal volume lung inflation [functional residual capacity (FRC) + 500 ml and FRC + 1 litre] on the change in pulmonary perfusion distribution. Changes in hydrostatic pressure distribution as well as transmural pressure distribution due to the change in lung height with tidal volume inflation are probably bigger contributors to the redistribution of pulmonary perfusion than the changes in pulmonary vasculature resistance caused by lung tissue stretch.

Effect of Posture on Regional Deposition of Coarse Particles in the Healthy Human Lung.

Background: Understanding the regional partition of deposition of inhaled particles within the lung is important for improving targeted delivery of inhaled aerosolized drugs. One factor affecting regional deposition is gravity. As the lung deforms under its own weight, changes in lung volume, in airway geometries, and in spatial patterns of ventilation distribution between postures have the potential to alter the regional distribution of deposited particles.

Inhaled nitric oxide alters the distribution of blood flow in the healthy human lung, suggesting active hypoxic pulmonary vasoconstriction in normoxia.

Hypoxic pulmonary vasoconstriction (HPV) is thought to actively regulate ventilation-perfusion (V̇a/Q̇) matching, reducing perfusion in regions of alveolar hypoxia. We assessed the extent of HPV in the healthy human lung using inhaled nitric oxide (iNO) under inspired oxygen fractions (FiO2 ) of 0.125, 0.

Validating the distribution of specific ventilation in healthy humans measured using proton MR imaging.

Specific ventilation imaging (SVI) uses proton MRI to quantitatively map the distribution of specific ventilation (SV) in the human lung, using inhaled oxygen as a contrast agent. To validate this recent technique, we compared the quantitative measures of heterogeneity of the SV distribution in a 15-mm sagittal slice of lung obtained in 10 healthy supine subjects, (age 37 ± 10 yr, forced expiratory volume in 1 s 97 ± 7% predicted) using SVI to those obtained in the whole lung from multiple-breath nitrogen washout (MBW). Using the analysis of Lewis et al.

Cardiogenic mixing increases aerosol deposition in the human lung in the absence of gravity.

Rationale: Exposure to extraterrestrial dusts is an almost inevitable consequence of any proposed planetary exploration. Previous studies in humans showed reduced deposition in low-gravity compared with normal gravity (1G). However, the reduced sedimentation means that fewer particles deposit in the airways, increasing the number of particles transported to the lung periphery where they eventually deposit albeit at a smaller rate than in 1G.

The heterogeneity of regional specific ventilation is unchanged following heavy exercise in athletes.

Heavy exercise increases ventilation-perfusion mismatch and decreases pulmonary gas exchange efficiency. Previous work using magnetic resonance imaging (MRI) arterial spin labeling in athletes has shown that, after 45 min of heavy exercise, the spatial heterogeneity of pulmonary blood flow was increased in recovery. We hypothesized that the heterogeneity of regional specific ventilation (SV, the local tidal volume over functional residual capacity ratio) would also be increased following sustained exercise, consistent with the previously documented changes in blood flow heterogeneity.

The gravitational distribution of ventilation-perfusion ratio is more uniform in prone than supine posture in the normal human lung.

The gravitational gradient of intrapleural pressure is suggested to be less in prone posture than supine. Thus the gravitational distribution of ventilation is expected to be more uniform prone, potentially affecting regional ventilation-perfusion (Va/Q) ratio. Using a novel functional lung magnetic resonance imaging technique to measure regional Va/Q ratio, the gravitational gradients in proton density, ventilation, perfusion, and Va/Q ratio were measured in prone and supine posture.

Spatial-temporal dynamics of pulmonary blood flow in the healthy human lung in response to altered FI(O2).

The temporal dynamics of blood flow in the human lung have been largely unexplored due to the lack of appropriate technology. Using the magnetic resonance imaging method of arterial spin labeling (ASL) with subject-gated breathing, we produced a dynamic series of flow-weighted images in a single sagittal slice of the right lung with a spatial resolution of ~1 cm(3) and a temporal resolution of ~10 s. The mean flow pattern determined from a set of reference images was removed to produce a time series of blood flow fluctuations.

Magnetic resonance imaging quantification of pulmonary perfusion using calibrated arterial spin labeling.

Unlabelled: This demonstrates a MR imaging method to measure the spatial distribution of pulmonary blood flow in healthy subjects during normoxia (inspired O(2), fraction (F(I)O(2)) = 0.21) hypoxia (F(I)O(2) = 0.125), and hyperoxia (F(I)O(2) = 1.

Vertical distribution of specific ventilation in normal supine humans measured by oxygen-enhanced proton MRI.

Specific ventilation (SV) is the ratio of fresh gas entering a lung region divided by its end-expiratory volume. To quantify the vertical (gravitationally dependent) gradient of SV in eight healthy supine subjects, we implemented a novel proton magnetic resonance imaging (MRI) method. Oxygen is used as a contrast agent, which in solution changes the longitudinal relaxation time (T1) in lung tissue.

Microgravity alters respiratory abdominal and rib cage motion during sleep.

The abdominal and rib cage contributions to tidal breathing differ between rapid-eye-movement (REM) and non-NREM sleep. We hypothesized that abdominal relative contribution during NREM and REM sleep would be altered in different directions when comparing sleep on Earth with sleep in sustained microgravity (microG), due to conformational changes and differences in coupling between the rib cage and the abdominal compartment induced by weightlessness. We studied respiration during sleep in five astronauts before, during, and after two Space Shuttle missions.

A method for the analysis of respiratory sinus arrhythmia using continuous wavelet transforms.

A continuous wavelet transform-based method is presented to study the nonstationary strength and phase delay of the respiratory sinus arrhythmia (RSA). The RSA is the cyclic variation of instantaneous heart rate at the breathing frequency. In studies of cardio-respiratory interaction during sleep, paced breathing or postural changes, low respiratory frequencies, and fast changes can occur.

Noninvasive beat-to-beat stroke volume computation during acute hydrostatic pressure changes in parabolic flight.

A three-element model of the cardiovascular system was used to monitor stroke volume (SV) changes during parabolic flight. Aortic blood flow was estimated from continuous arterial finger pressure and SV computed by integrating simulated aortic flow during each systole. SV was significantly higher in microgravity (microgravity) compared to 1 G whereas in hypergravity (hG), SV was significantly lower.

Dynamics of blood pressure, pulse wave transit time and systolic time intervals during acute gravity changes induced by parabolic flight.

To investigate cardiovascular adaptation to transient microgravity (microgravity), we measured RR intervals (RRI), arterial blood pressure (BP), pulse wave transit time (PTT) and systolic time intervals (STI) during parabolic flight. Our results demonstrate that during microgram RRI, BP and PTT are subject to a rapid adaptation likely mediated by the baroreflex whereas STI changes with microgravity but does not present further adaptation.