FIELD OF THE INVENTION
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The present invention pertains generally to medical equipment and more particularly to a compressor powered mechanical ventilator device for delivering respiratory ventilation to a mammalian patient.
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OF THE INVENTION
A. Principles of Mechanical Ventilation
In many clinical settings mechanical ventilators are used to facilitate the respiratory flow of gas into and out of the lungs of patients who are sick, injured or anesthetized.
In general, mechanical ventilators provide a repetitive cycling of ventilatory flow, each such repetitive cycle being separated into two phases—an inspiratory phase followed by an expiratory phase.
The inspiratory phase of the ventilator cycle is characterized by the movement of positive-pressure inspiratory flow of gas through the ventilator circuit and into the lungs of the patient. The expiratory phase of the ventilatory cycle is characterized by cessation of the positive pressure inspiratory flow long enough to allow lung deflation to occur. The exhaled gas is vented from the ventilator circuit, typically through an exhalation valve. In patient whose lungs and thoracic musculature exhibit normal compliance, the act of exhalation is usually permitted to occur spontaneously without mechanical assistance from the ventilator.
It is sometimes desirable to control the airway pressure during exhalation to maintain a predetermined amount of positive back pressure during all, or a portion of, the respiratory cycle. Such techniques are often utilized to treat impairments of lung capacity due to pulmonary atelectasis or other factors.
The mechanical ventilators of the prior art have been grouped under various classification schemes, based on various criteria. In general, mechanical ventilators may be grouped or classified according to the parameter(s) which are utilized for a) triggering, b) limiting and c) terminating (e.g., cycling) the inspiratory phase of the ventilator cycle.
“Triggering” is the action that initiates the inspiratory phase of the ventilator cycle. The initiation of the inspiratory phase may be triggered by the ventilator or the patient. The variables and/or parameters which are utilized to trigger the beginning of the inspiratory phase include: time (i.e., respiratory rate), the commencement of spontaneous inhalation by the patient and/or combinations thereof.
“Limiting” of the inspiratory phase refers to the manner in which the inspiratory gas flow is maintained within prescribed ranges to optimize the ventilation of the patient's lungs. The limiting variables and/or parameters are typically controlled by the ventilator; but may change as a result of patient effort and/or physiologic variables such as lung compliance and airway resistance. The variables and/or parameters which are utilized or limiting the inspiratory phase include flow rate, airway pressure and delivered volume.
“Terminating” or “cycling” of the inspiratory phase of the ventilator cycle refers to the point at which the inspiratory flow is stopped and the ventilator and/or patient are permitted to “cycle” into the expiratory phase. Depending on the ventilator control settings, the termination of the inspiratory phase may be brought about by the ventilator or the patient. The variables and/or parameters which are utilized to terminate the inspiratory phase include: time; peak airway pressure; and/or tidal volume (Vt).
B. Mechanical Ventilation Modes Utilized
In Modern Clinical Practice
In addition Mechanical ventilators are utilized to deliver various “modes” of mechanical ventilation, the particular mode of ventilation being selected or prescribed based on the clinical condition of the patient and the overall objective (i.e., long term ventilation, short term ventilation, weaning from ventilator, etc. . . . ) of the mechanical ventilation.
I. Ventilation Modes
i. Intermittent Mandatory Ventilation (IMV)
Intermittent Mandatory Ventilation is a ventilation mode wherein a spontaneously breathing patient receives intermittent mechanical inflation supplied asynchronously by the ventilator.
ii. Synchronized Intermittent Mandatory Ventilation (SMIV)
Synchronized Intermittent Mandatory Ventilation is a ventilation mode wherein a spontaneously breathing patient receives occasional mandatory ventilatory breaths. Mandatory ventilator breaths are synchronized with the patient\'s spontaneous inspiratory efforts.
iii. Controlled Mechanical Ventilation (CMV)
Controlled Mechanical Ventilation (CMV) is a ventilation mode wherein mechanical breaths are delivered to the patient at time intervals which are unaffected by patient efforts. Controlled Mechanical Ventilation is typically utilized in patients who are not breathing spontaneously.
iv. Assist/Control Ventilation (A/C)
Assist/Control Ventilation (A/C) is a ventilation mode wherein the patient is able to volitionally alter the frequency of mandatory ventilator breaths received, but can not alter the flow and title volume (Vt) of each ventilator breath received. Controlled, mandatory breaths are initiated by the ventilator based on the set breath rate. In addition, the patient can demand and trigger an assist breath. After successful triggering of an assist breath, the exhalation valve is closed and gas is delivered to the patient to satisfy the preset tidal volume, peak flow and wave form.
C. Breath Types Utilized in Modern Clinical Practice
Breath types are typically classified according to the 25 particular functions which control:
b) limiting; and
c) cycling of each breath delivered by the mechanical ventilator, as described and defined hereabove.
Typical breath types and ventilator parameters utilized in modern clinical practice include the following:
i. Machine-Cycled—Mandatory Breath