Biomedical subjects

V J Lamb

Publications and source records attributed to V J Lamb.

3 recordsLinked to original sources

PubMed1990

Breath-stacking increases the depth and duration of chest expansion by incentive spirometry.

Although the objective of incentive spirometry is to achieve and hold high lung volumes, many patients with pain or weakness are unable to sustain the effort needed to perform effective exercises. We questioned whether using a one-way valve to prevent exhalation would allow rest between inspiratory efforts and cause volume to cumulate during successive tidal efforts, improving both the depth and duration of the inspiratory maneuver. We studied 26 cooperative but naive patients recovering from surgery, trauma, or critical illness whose pain or weakness impaired ability to achieve and sustain deep inspiration. All subjects breathed via mouthpiece from a spirometer prefilled with 100% oxygen. Three different maneuvers were performed in random order by all subjects: (1) standard inspiratory capacity without valve or inspiratory hold, (2) inspiratory capacity (IC) with breathholding aided by a one-way valve, and (3) uncoached breath-stacking, during which successive tidal breaths were cumulated by one-way valving. A fourth maneuver was added in the last 13 subjects studied: an initial coached IC effort with subsequent valved stacking of tidal efforts. When compared with IC, "breath stacking" (valved) maneuvers increased inspired volume by an average of 15 to 20% (p less than 0.05). More importantly, there was a severalfold increase in the time over which high lung volume was sustained (p less than 0.001). Our results indicate that one-way valving helps to achieve and sustain deep inspiration, even in uncoached patients.

Humans↗

PubMed1988

External work output and force generation during synchronized intermittent mechanical ventilation. Effect of machine assistance on breathing effort.

We measured the mechanical work performed by 12 acutely ill patients during synchronized intermittent mandatory ventilation to determine the influence of volume-cycled machine assistance on inspiratory timing, respiratory muscle force development, and external work output. The frequency and tidal volume of spontaneous breaths increased at lower levels of mechanical ventilation, but inspiratory time fraction did not vary across the spectrum of machine support. As machine support was withdrawn, inspiratory work and pressure-time product increased progressively for both spontaneous and assisted breathing cycles. On a per cycle basis, work output was greater for assisted than for spontaneous breaths at all levels of comparison. Although the mean pressure developed by the patient during assisted cycles averaged approximately equal to 20% less than during adjacent unassisted cycles, contraction time averaged approximately equal to 20% longer, so that the pressure-time products were nearly equivalent for both types of cycle. Two indices of force reserve indicated that our patients taxed their maximal ventilatory capability at all but the highest levels of support. We conclude that under the conditions of this study the ventilatory pump continued to be active at all levels of machine assistance. Although work per liter related linearly to the proportion of minute ventilation borne by the patient, force generation differed little for spontaneous and machine-aided breaths at any specified level of support. Whether judged on the basis of mean developed pressure (work per liter of ventilation) or pressure-time product, little effort adaptation to volume-cycled machine assistance appears to occur on a breath-by-breath basis.

Humans↗

PubMed1986

Involuntary breath-stacking. An alternative method for vital capacity estimation in poorly cooperative subjects.

Performed correctly, the vital capacity (VC) is a useful indicator of the mechanical properties of the thorax and of neuromuscular performance. Unfortunately, its use is often limited by impaired comprehension, altered mental status, or inability to sustain forceful effort. Our purpose was to develop a measure of VC independent of subject cooperation. We estimated the subcomponents of VC (inspiratory capacity (IC) and expiratory reserve volume (ERV], using one-way valving of an external circuit to enforce cumulation or elimination of the tidal breaths stimulated by endogenous ventilatory drive. When configured to measure IC, gas entered the chest incrementally, until tidal effort became insufficient to overcome thoracic recoil. Valve rearrangement permitted analogous estimation of ERV. We tested the validity of this method in cooperative but naive subjects by comparing the VC measured in standard fashion (VCC) to the breath-stacked estimate (VCS). Thirty normal subjects and 20 ambulatory patients with diverse causes for respiratory impairment were studied. Peak and mean values of VCS correlated strongly with the corresponding values of VCC (r greater than or equal to 0.91). The coefficient of variation for sequential V VCS determinations (approximately equal to 5.5%) was comparable to that observed for VCC (approximately equal to 3.5%) in both subject groups, indicating acceptable reproducibility of the involuntary VCS measurement. VCS maneuvers were quickly completed and well tolerated. Involuntary breath-stacking may provide a useful estimate of VC in clinical settings where conventional methodology cannot be confidently applied.

Adult↗