Morphometric assessment of surface conformation as an estimate of roughness.

One of the standard methods for assessing the roughness of a material subjected to wear uses the surface arithmetic means and root-mean-square deviation. However, these parameters often do not provide a qualitative assessment of the difference in materials worn under the same conditions of load and elapsed time. The profile and surface roughness parameters are frequently inconsistent. Such measurements are also required to determine the wear characteristics of various materials under different conditions. A morphometric assessment of wear characteristics, based on the surface area fraction of localized deviations in the surface texture and stress fractures, is provided, and clearly indicates the observed difference.

Startle-evoked changes in diaphragmatic activity during wakefulness and sleep.

Tonic inhibition of some respiratory muscles occurs as part of the generalized muscle atonia of rapid-eye-movement sleep (REMS). A second type of inhibition of the diaphragm during REMS, fractionations, consists of brief pauses in the diaphragmatic electromyogram (DIA EMG) in association with phasic events. Because motor inhibition can occur as part of the startle response, and the brain is highly activated during REMS, we hypothesized that the neural basis of the fractionations might be activation of a startle network. To test this hypothesis, tone bursts (100 dB, 20-ms duration at 15-s intervals) were applied to cats at a fixed inspiratory level in the DIA moving average during REMS, non-rapid-eye-movement sleep (NREMS), and wakefulness. Parallel sham studies (no tone applied) were obtained for each state. The response of the DIA EMG was averaged over 100 ms by using the tone pulse as a trigger, and the following parameters of the DIA EMG were measured: latency to peak and/or nadir, increment or decrement in activity, and duration of peak and/or nadir. After a tone, all five animals studied displayed a profound suppression of DIA activity during REMS (latency to nadir 42.4 +/- 10.0 ms, duration of suppression 35.9 +/- 17.6 ms). Similarly, DIA activity was suppressed in all cats during NREMS (latency to nadir 40.9 +/- 13.3 ms, duration 23.9 +/- 13.4 ms). An excitatory response was observed in only two cats during NREMS and wakefulness. The similarity of startle-induced DIA EMG pauses to spontaneous fractionations of DIA activity during REMS suggests that the latter result from activation of a central startle system.

Spectral and coherence analysis applied to sleep apnea.

The various mechanisms that have been proposed to explain sleep apnea in the elderly are examined. Spectral analysis of the electroencephalogram (EEG), not only in the frequency domain using autoregressive algorithms and the fast Fourier transform, but also in the time domain with comb filters and period-amplitude (PA) analysis, is discussed. The PA features, in particular, may provide an improved basis for the coherence function between ventilation and the state-dependent input.

Morphometric measurement of local curvature of the alveolar ducts in lung mechanics.

We have performed partial serial reconstructions of an acinus of the rabbit lung and determined the apparent existence of numerous heterogeneities in length, diameter, and local curvature in individual generation branches of the lung. We believe that structural changes during respiratory movements may include changes in the length and diameter of the whole duct. Alveoli are seen to be side differentiations secondary to the ducts in the gas-exchanging parenchyma of the rabbit lung. We have developed a technique for measuring local curvature in simple reconstructed ducts from the average of the integral curvation of the section contour. The contour curvature is measured from the chain code representation of the sampled contour from digital image analysis. The stereological requirements of an unbiased and random selection of contours is approached here by the random orientation of the individual alveoli of a single duct. Over 700 sections through the last four airway generations (alveolar ducts) at 3-micron intervals were analyzed. The average integral curvature ranges from 7.7 to 9.5 (mean 8.9) mm-1 for sixth- and seventh-generation branches from the start with volumes for the segments from 0.022 to 1.198 (mean 0.497) mm3.

Spectral analysis of ventilation in elderly subjects awake and asleep.

We studied the periodicities of ventilation in elderly subjects using digital comb filtering. Two groups of subjects were studied, those with and without sleep apnea. Measurements were made in wakefulness, stage 1-2 sleep, and where possible in stage 3-4 sleep. For each of the digital filters we calculated the average power of the oscillatory output. To compare subject groups we first specifically determined the average power in the filter with the maximum output. The mean of this measurement was greater in elderly subjects with apnea compared with those without apnea, both during wakefulness and stage 1-2 sleep. In both groups of subjects the cycle time of the major ventilatory oscillations was on the order of 40-60 s. There was no difference in this cycle time between the two groups of subjects in wakefulness or stage 1-2 sleep. Thus, whereas similar oscillatory processes occur in subjects with and without apnea, it is the magnitude of the oscillation that differs between the two groups. These conclusions are supported by analysis of the output of individual filters of the digital comb filter. In both groups, stage 1-2 sleep produced significantly increased oscillations in ventilation. Both in wakefulness and stage 1-2 sleep, significantly greater periodicities occurred in the apneic compared with the nonapneic group. In the few subjects who had sufficient data in stage 3-4 sleep for spectral analysis, ventilatory oscillations were virtually absent in this state. Our data suggest that subjects who develop apnea during sleep have an increased propensity for periodic breathing even while awake.

Effects of lung inflation on the excitability of dorsal respiratory group neurons.

The effect of lung inflation on the excitability of inspiratory neurons of the dorsal respiratory group was studied in decerebrate, paralyzed, artificially ventilated cats. Variations in the antidromic latency (AL) were used as a measure of the changes in excitability. The antidromic responses of single cells were recorded extracellularly during electrical stimulation (20 Hz) of their spinal axons. Single-breath test inflations were delivered at the onset of inspiration (I) or expiration (E), and then maintained for the duration of that respiratory phase. In the absence of inflation during E, most of the inspiratory cells underwent progressive lengthening of the AL, indicating inhibition or disfacilitation. This effect was stronger in I beta than in I alpha cells but there was considerable overlap. In every cell (21 I alpha, 17 I beta), inflation during E caused a prompt AL shortening (excitation or disinhibition) that was evident in single tests. On average, I beta neurons were more strongly excited by the test inflation during E, but again there was considerable overlap. The excitation was maintained for the duration of the inflation, indicating that pulmonary stretch receptor afferents (PSR) were involved. The response to slow inflations (that preferentially excite PSR) was a progressive shortening of the AL that mirrored the increase in lung volume. The results emphasize the qualitative similarity in the responses of I alpha and I beta neurons to lung inflation and in their excitability changes during normal respiratory cycles.

Applications of computerized interactive morphometry in pathology: I. Tracings and generation of graphic standards.

We have studied the use in anatomic pathology of a computerized interactive morphometry system and conditions for reliability and proper interpretation of data obtained by tracings. Because of the ease of operation and direct visualization of the tracings, we prefer touch-sensitive screens to digitizing tablets as optimal interactive peripherals. Because touch screens have fewer sampling points (256 X 256) than tracing tablets, we studied the relationship between point density and accuracy of length and area measurements by tracing models of known dimensions on the touch screen by experimenting with different step sizes ranging from every second to every sixth valid sampling point; we obtained excellent results with step size 6 followed by two-fold smoothing by two-dimensional filtering. We conclude that because of staircase formation, a high point density may be more of a liability than an asset and that the touch screen is satisfactory. By tracing closed figures of variable shapes but known areas we observed that area measurements may be unreliable with certain irregular shapes and we discuss how perimeter to area ratios can be used to compute surface to volume ratios. Finally, the generation of simple calibrated graphic standards over routine pathologic slides makes the system useful for fast diagnostic applications.

Ventilatory and arousal patterns during sleep in normal young and elderly subjects.

Since elderly subjects have lower chemosensitivity, we postulated that ventilation might be more state dependent in the elderly. To address this we investigated the changes in ventilation, measured by respiratory inductive plethysmography, with sleep in 12 healthy young (19-29 yr) and 13 elderly (greater than 65 yr) subjects. Ventilation was measured in representative periods in each sleep state. These data showed that there is no difference between the elderly and the young either in mean ventilation or in the variability of ventilation awake or in the different states of sleep. In both groups ventilation was variable in stage 1-2 sleep and least variable in stage 3-4 sleep. The variability in stage 1-2 sleep was due to periodic breathing (cycle time approximately 45 s) in both age groups. Although within a sleep state no differences were observed, over the night of study the elderly behaved differently from the young. Apneas occurred more frequently in the elderly, and 5 of 13 elderly met the criteria for sleep apnea syndrome compared with 1 of 12 young subjects. Apneas tended to occur predominantly in stage 1-2 sleep and seem to be an exaggeration of the periodicity that is typical of this state. Four of the elderly with apnea remained in this stage of sleep throughout the night of study. The apneic episodes usually terminated with an electroencephalogram arousal that occurred prior to or simultaneously with the onset of ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Applications of a hand-held computer in critical care medicine.

Hand-held computers provide a reasonable alternative to desk-top computers in critical care units because of their size and affordability. The applications described include specific examples of software to perform hemodynamic calculations, intravenous flow rate calculations, and respiratory calculations. This software has been used for several years and has been found to be very useful.

Digital image tiles: a method for the processing of large sections.

Segmentation of large areas of light microscopic slides into N by N fields, and each of these fields into M digital image tiles, allows the scanning, storage and digital processing of large images. Any of the original N2 fields or composites of M adjacent tiles can be recalled to the video display for analysis. Developed procedures for use on a microscope equipped with a precision scanning stage allow registration of the image coordinates (X-Y) for any original or composite field and the alignment of one of these fields along the depth (Z) axis by means of external, machined fiducial marks in serial sections. To facilitate work whenever unavoidable, we have incorporated methods for digital image panning and zooming (changes of magnification) and discuss their use and implications.

Methods in laboratory investigation. Digital reversal and enhancement of negatives in video-based interactive morphometry.

We describe a system for the digital reversal of negatives in interactive morphometry. Minimum requirements, in addition to a high-resolution black and white video camera and monitor, are a readily available digital video frame store and a computer system as simple as a microprocessor-based personal computer. In a video-based analysis system, the addition of a digital image memory device and computer obviates the time and expense of photographic processing of the large number of negatives to positive prints required for an appropriate sampling size in morphometry. Additionally, the enhancement of digital images to recover details in the negative is feasible. This study represents a part of a continuing effort to develop an efficient, interactive morphometry system that encourages the use of a large number of random samples by simplifying processing.

An arterial blood gas interpretation program for hand-held computers.

Because of its portability, the hand-held computer can be easily used at the bedside to perform mathematical computations and assist with patient care decision making. This paper describes applications software for arterial blood gas interpretation with the hand-held computer. From the arterial blood gas values entered, the program calculates the arterial/alveolar PO2 ratio (a/A PO2), provides an interpretation of oxygenation, a/A PO2, ventilation, and acid-base status, and makes suggestions for therapy. This program can be used for the individualized bedside teaching of students and others with limited experience in arterial blood gas interpretation.

The use of touch-sensitive screen in interactive morphometry.

We propose the use of a touch-sensitive screen as a tool to facilitate acquisition of data both in point counting and morphometric planimetry. It obviates the use of a 'correspondence image' required with many planimetric devices in which the means for data acquisition and display are separate. The touch-sensitive screen offers operational advantages over the light pen. The characteristics of this new graphical input device, its assembly and basic operational considerations are introduced and discussed.

Effect of aging on ventilatory response to exercise and CO2.

Studies were performed to determine the effects of aging on the ventilatory responsiveness to two known respiratory stimulants, inhaled CO2 and exercise. Although explanation of the physiological mechanisms underlying development of exercise hyperpnea remains elusive, there is much circumstantial evidence that during exercise, however mediated, ventilation is coupled to CO2 production. Thus matched groups of young and elderly subjects were studied to determine the relationship between increasing ventilation and increasing CO2 production (VCO2) during steady-state exercise and the change in their minute ventilation in response to progressive hypercapnia during CO2 rebreathing. We found that the slope of the ventilatory response to hypercapnia was depressed in elderly subjects when compared with the younger control group (delta VE/delta PCO2 = 1.64 +/- 0.21 vs. 2.44 +/- 0.40 l X min-1 X mmHg-1, means +/- SE, respectively). In contrast, the slope of the relationship between ventilation and CO2 production during exercise in the elderly was greater than that of younger subjects (delta VE/delta VCO2 = 29.7 +/- 1.19 vs. 25.3 +/- 1.54, means +/- SE, respectively), as was minute ventilation at a single work load (50 W) (32.4 +/- 2.3 vs. 25.7 +/- 1.54 l/min, means +/- SE, respectively). This increased ventilation during exercise in the elderly was not produced by arterial O2 desaturation, and increased anaerobiasis did not play a role. Instead, the increased ventilation during exercise seems to compensate for increased inefficiency of gas exchange such that exercise remains essentially isocapnic. In conclusion, in the elderly the ventilatory response to hypercapnia is less than in young subjects, whereas the ventilatory response to exercise is greater.

A spirometry/interpretation program for hand-held computers.

The recent introduction of the hand-held computer has provided an important new tool for the medical team. The device is inexpensive, portable, and operator-programmable in BASIC. We describe software for a spirometry program with computer-generated interpretation as an example of numerical calculation and logical decision making.

Effect of simple anthracite pneumoconiosis on lung mechanics.

A respiratory questionnaire was administered to 20 miners with simple anthracite coal workers' pneumoconiosis (CWP) and ten normal subjects. Lung function studies which included lung mechanics and small airways disease measurements were also performed. Seventeen of the miners admitted to having symptoms of bronchitis. No significant differences were demonstrated between the two groups for vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and three seconds (FEV3), midmaximal flow rate (FEF25-75%), and peak flow rate (PEFR). A significant decrease in the maximum expiratory flow rate at 50 percent of vital capacity (V max50%) was detected; however, this was not evident when the flow rate was corrected for lung volume. Also, there were no significant differences in lung volumes, diffusing capacity (DCO) and diffusion coefficient (DCO/TLC). The mean static expired compliance (Cstate) was significantly increased in the anthracite miners, but no difference in specific compliance (Cstate/FRC) could be demonstrated. Also, no significant differences were detected in the mean values of any of the tests of small airways disease. There is little evidence of significant alterations in lung mechanics or small airway narrowing in miners with simple anthracite pneumoconiosis.

Effect of aerosolized histamine on occlusion pressure and ventilation in humans.

To define further the mechanism by which inspiratory neural activity is increased in asthma, we studied the effect of aerosolized histamine on occlusion pressure (P100) and ventilation in conscious humans while end-tidal CO2 partial pressure was maintained at a constant, slightly hypercapnic level. The dose of histamine we employed varied from subject to subject but was such that it produced a 70% reduction in specific airway conductance in each subject. In 9 of the 13 subjects tested, inhaled histamine significantly increased P100. This increase was not due to changes in functional residual capacity, which was not affected by aerosolized histamine. Inhalation of isoproterenol abolished the effects of histamine on specific airway conductance and P100. Anesthesia of the airways by lidocaine eliminated the effect of histamine on P100 but did not alter the magnitude of the change in specific airway conductance produced by histamine. We conclude that the increase in occlusion pressure seen after the inhalation of histamine in humans depends on both contraction of bronchial smooth muscle and stimulation of airway receptors.

Effects of aging on ventilatory and occlusion pressure responses to hypoxia and hypercapnia.

Studies were performed to examine the decrease in ventilatory response to hypoxia and hypercapnia in the elderly and to explore its etiology. For this purpose, matched groups of normal elderly (65 to 79 yr of age) and young subjects were used. Standard pulmonary function tests were supplemented in both groups by determination of total respiratory compliance and the ventilatory responses to hyperoxic hypercapnia and isocapnic hypoxia using rebreathing methods. While testing the ventilatory responses, we recorded minute ventilation and its components, as well as mouth occlusion pressures, and rib cage and abdominal-diaphragmatic compartmental ventilation (magnetometry). We found that ventilatory responses to both hypercapnia and hypoxia were reduced in the elderly by approximately 50%. These reductions were not related to any change in control of respiratory timing, but to a large reduction in mean inspiratory airflow. The reduced airflow could not be attributed to alterations in pulmonary mechanics since the differences in mechanics between the groups were small. Instead, since the occlusion pressure responses to hypercapnia and hypoxia were reduced in the elderly proportionately to the ventilatory responses, reduction in neuromuscular inspiratory output was likely to be the major factor.