Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
1997-12-11
2002-10-01
Weiss, John G. (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204260, C128S207140
Reexamination Certificate
active
06457472
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ventilatory support system, and more particularly relates to a method and apparatus for providing a controlled flow of breathing gas to a patient based on the function of the patient's upper airways which vary over time in relation to the physiological requirements of the patient.
BACKGROUND INFORMATION
There are many clinical disorders that are characterized by the failure of patients to maintain adequate ventilation. In general, ventilation can be compromised in one of two ways. First, there are patients who cannot breathe adequately due to excessive mechanical loads on the ventilatory apparatus or weakness of the respiratory muscles. Examples of such mechanical loads include upper airway obstruction in obstructive sleep apnea, bronchial obstruction in asthma and chronic obstructive pulmonary disease, and reductions in lung or chest wall compliance in diseases involving the pulmonary parenchymal and chest wall. Second, ventilation may be compromised by a failure of neuromuscular mechanisms in patients who may have disorders involving the central nervous system or phrenic nerves. Regardless of etiology, each of these disorders is associated with reduced levels of ventilation.
In patients with reduced levels of ventilation, ventilation can be augmented by blowing air into the airway. In one approach, air can be applied to help wash CO
2
out from the airways. When an additional source of air is applied to the central airways, ventilation may fall because less is required to eliminate CO
2
. Currently, two such methods are utilized clinically to aid CO
2
washout from the airways. In intubated patients, air is administered either continuously or during expiration by a process known as tracheal gas insufflation (TGI). Alternatively, air can be administered through a thin transtracheal cannula in non-intubated, spontaneously breathing patients. Current evidence suggests that low flow rates up to 5 to 6 liters/min can wash out CO
2
and reduce a patient's ventilatory requirements. For CO
2
washout to occur, insufflated air must vent freely to atmosphere. With continuous transtracheal insufflation (TTI), therefore, CO
2
washout allows patients to reduce ventilation without increasing CO
2
.
In another approach, mechanical ventilation can be instituted to augment ventilation. Positive pressure ventilation is the most common form of mechanical ventilation. It is characterized by intermittent application of positive pressure to the airway. When airway pressure is increased, the lungs inflate. Deflation occurs passively after allowing the airway pressure to fall. Therefore, positive pressure can be applied intermittently to the airway to augment ventilation in patients who cannot maintain normal levels of ventilation on their own. Various mechanisms have been developed to augment ventilation with positive pressure devices, including endotracheal tubes, tracheostomy tubes and nasal/oronasal masks. In each example, a tight seal is required between the ventilator and the patient's airway, thereby preventing leakage of air when positive pressure is applied. As a result, these interfaces are relatively intrusive, and interfere with speech, swallowing, normal breathing patterns, and normal sleep/wake rhythms.
Obstructive sleep apnea is one example of a condition in which there is cyclic occlusion and reopening of the pharynx, which results in the obstruction of airflow during sleep, hypoxic episodes and daytime somnolence. Two general approaches have been utilized to treat this disorder. First, methods have been devised to relieve pharyngeal airflow obstruction. At present, nasal continuous positive airway pressure (nCPAP) is the most effective way to relieve obstruction. It is applied via a nasal mask and maintains pharyngeal patency during sleep. CPAP is most effective when a tight seal is maintained between the patient's airway and the nasal mask. U.S. Pat. Nos. 5,551,419, 5,540,219, Re. 35,295, 5,535,738, and 5,490,502 disclose the use of such CPAP devices. However, despite its low incidence of side effects CPAP is often not well tolerated, and many patients do not adhere to therapy because the tightly applied nasal mask causes claustrophobia (Kribbs et al.,
Am. Rev. Respir. Dis.,
Vol. 147, 1993). The present invention, however, does not require such a tight seal. Rather than relieving upper airway obstruction as nasal CPAP, it works in concert with the patient's breathing efforts and the natural tendency of the upper airway to collapse and obstruct the exit of airflow from the lungs.
When relief of pharyngeal obstruction is not achievable with nasal CPAP, tracheostomy provides an alternative breathing route during sleep which bypasses the pharynx. It is effective in treating this disorder because it provides a widely patent bypass route for breathing. With tracheostomy, air can be inspired and expired freely from/to atmosphere irrespective of the state of the upper airway patency. Although highly effective in treating apneic patients, tracheostomy is associated with significant morbidity from repeated airway infections, intractable cough, speech difficulties and disfigurement. Because of its high morbidity, tracheostomy is rarely considered by either patients or physicians to be an acceptable therapeutic alternative, except when sleep apnea is life-threatening. The present invention avoids these adverse effects, yet provides a mechanism for both inspiration and expiration that utilizes the upper airway to coordinate the pattern of airflow.
Another proposed method is to provide long-term supplemental oxygen therapy via a thin transtracheal cannula through which a low flow rate of oxygen is delivered intratracheally to patients with lung disease. U.S. Pat. Nos. 5,181,509 and 5,090,408 disclose examples of such cannulas. Clinical reports and experience with this type of cannula has shown it to be an effective, well tolerated oxygen delivery method. However, the low flow rate of oxygen is not sufficient to provide satisfactory ventilatory support to patients.
U.S. Pat. Nos. 5,101,820 and 5,279,288 to Christopher disclose the use of a transtracheal catheter to provide a continuous high flow rate of oxygen-containing gas to a patient. However, there are disadvantages associated with the continuous delivery of gas to patients, such as spasm of the vocal cords and closure of the upper airway. This can result in the rapid buildup of excessive pressure in the trachea and lungs of the patient (pneumothorax and pneumomediastinum) and alterations in the breathing pattern which perpetuate problems with sleep disruption and daytime hypersomnolence.
The disclosure of each of the patents cited above is incorporated herein by reference.
The present invention has been developed in view of the foregoing and to overcome other deficiencies of the prior art.
SUMMARY OF THE INVENTION
The present invention provides a ventilatory support system which controls the flow of breathing gas to a patient based on the function of the patient's upper airway and his or her ventilatory needs. Gas pressure in the trachea of the patient is measured, and the delivery of breathing gas to the patient is controlled based on the sensed gas pressure. Depending on the upper airway function of the patient, a tracheal gas pressure limit and a breathing gas flow rate value are established. When the tracheal gas pressure limit is reached, the flow of breathing gas is reduced or terminated. The flow of breathing gas is subsequently resumed either immediately, after a delay period, or after the tracheal gas pressure falls to a predetermined level. The system thus provides a feedback loop using tracheal pressure which reflects a patient's ventilatory and upper airway status in order to control the flow of breathing gas.
An important feature of the present invention is that the upper airways of the patient constitute an integral part of the breathing circuit. The upper airways serve as a valve which controls whether the applied tracheal breath
Schwartz Alan R.
Smith Philip L.
Pietragallo Bosick & Gordon
The Johns Hopkins University
Towner Alan G.
Weiss John G.
Weiss, Jr. Joseph F.
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